The teaching reform of digital signal processing emphasizes the role of graphics in understanding and memorizing knowledge, and the role of mind map in integrating knowledge points. Using the flip classroom to increase teaching interaction, which can improve the effectiveness of teaching and stimulate students’ interest in learning. Introduction China is in an upsurge of innovation, especially in the fields of information technology, emerging industries, robots and so on. With the gradual disappearance of "demographic dividend", the prospect of "engineer dividend" is very bright. Big data, artificial intelligence and Internet are the main trends of the development of modern information technology, while digitalization is the research foundation. Therefore, the course of Digital Signal Processing has become the main course for almost all electronic, electrical and information majors, such as electronic information, communication engineering, automatic control and computer. Teaching the course of Digital Signal Processing well is very important to train students to be qualified engineers. Digital Signal Processing is usually considered as a course with many mathematical contents. One of the remarkable features is its abstraction of concepts, numerous mathematical formulas and complex derivation. In the process of teaching, teachers often focus on the deduction of mathematical formulas, while ignoring the practical application of the course itself. Many students, especially those in general applied undergraduate colleges and universities, are unable to understand and clarify the course, so be tired even afraid of learning. Therefore, in the course of teaching, the main task of the teacher is to make the abstract theory easy to understand, to make the complex mathematical deduction simple and clear, to summarize the numerous knowledge points, and to facilitate memory. Many teachers have carried out in-depth teaching reform research on this course. Hao Xiaoli [1] discussed how to construct the new curriculum system of signal processing courses, integrate and update the teaching content, and put forward the specific methods of teaching reform. Xie Shouqing [2] and others use software to optimize the teaching of integrated signal and system and digital signal processing courses, so as to visualize the basic principles. Hanjian [3] et al. use speech signal as processing object, carry out frequency conversion and digital filtering of speech signal, cover the main knowledge points of this course, improve students' practical ability and innovative consciousness in engineering, and achieve good results in teaching. According to the actual situation of Department of Electronic Information Engineering in Beijing Institute of Graphic Communication, this paper explores the teaching reform of digital signal processing course by introducing graphics and mind map into teaching and increasing teaching interaction by using flipping classroom mode. Emphasizing the Role of Graphics in Understanding and Memorizing Knowledge Bruner put forward the importance of learning knowledge structure that "unless one thing is put into a constructed model, it will soon be forgotten. Detailed information is stored in memory by means of a simplified way of expressing it. "If the acquired knowledge is not connected by a perfect structure, it will be mostly forgotten".[4] According to the teaching practice and the characteristics 239 of the course, the graphical teaching method is proposed in the teaching. The knowledge points are interpreted in the form of graphs or flow charts, so as to cultivate students' ability to construct knowledge structure, so as to achieve the goal of memory. For example, complex exponential signal is a very important basic signal in signal analysis theory, and can be used to describe various basic signals, such as DC signal, exponential signal, sine or cosine signal, and sine and cosine signals with growth or attenuation. Complex exponential signals can simplify many operations and analyses. If a complex exponential signal is input to a system, the output must also be a complex exponential signal, and the amplitude of the output signal is the square sum of the real part and the imaginary part of the response, and the phase of the output signal is the arc tangent of the ratio of the imaginary part to the real part. Understanding the physical meaning of complex exponential signals t j e is crucial to understanding the Euler formula and five major transformations of Fourier transform (FT). During teaching, the complex exponential signal t j e is illustrated graphically as a unit rotation vector with zero initial phases on the complex plane. The projection of the vector on the real axis is t cos , the projection on the imaginary axis is t sin : Figure 1. Illustrates complex exponential signals. The figure above not only gives students an intuitive impression, but also obtains the Euler's formula in a logical way, as well as some special complex exponential values, which are often used in some calculations, especially in the derivation of Fast Fourier Transform. t j t e t j sin cos (1) 1 2 k j e , 1 j e , 1 2 k j e , j e j 2 , j e j 2 (2) Fig. 1 can also easily explain why complex exponential signals are periodic, and further leads to the concept of Fourier series: the continuous periodic signals are expanded into a series of linear combinations of complex exponential signals with harmonic relations. When the period of periodic signals is extended to infinity, the expansion of aperiodic signals is obtained, which is Fourier transform. Continue expand j to complex plane, which means j s , we will get complex frequency domain Fourier transform Laplace transform (LT). The above concepts are sorted out in Table 1. The knowledge structure is clear. Various transformations compare and verify the formulas to help students analyze and memorize. The table takes square wave signal and its spectrum as an example, eliminating the longitudinal axis and other parameters, showing the waveform in a simplest way, highlighting the characteristics of signal and spectrum, and facilitating teachers' blackboard writing. j