Loudness describes the sound intensity sensations of the human hearing. A study about loudness calculation which is based on the Moore model shows us that starting from the mechanism of human`s ear, the basic principle and calculation skills of algorithm have been researched. By using Matlab to optimize the algorithm, the specific loudness curve and loudness level of any audio file can be calculated; equal-loudness curve by using Steffensen method is calculated compared with that from the acoustic standard, In order to validating the program. The loudness of the sewing machine under different conditions is calculated.