With the deep analysis on the rotational speed measurement and the error existed in the measurement process at present, this paper introduces a high precision rotational speed measurement system based on infrared sensor and microcontroller. This system combines with improved measuring method. The sensor is an infrared photoelectric sensor, and uses its characteristics of the autocollimator ensured accuracy of measurement. The photoelectric sensor outputs weak voltage pulse signal when it receives the reflected infrared light. And then the signal is processed by double-reversed amplification and twice pulse shaping circuit. The system uses the relevant logic functions of a D-type flip-flop to control two 16-bit microcontroller chip timing/counter turned on and off simultaneously, and calculates the rotation speed. At last, the result is displayed on LED by Microcontroller. This measurement system has high accuracy, fast sampling speed and wide measuring range.