Abstract: Muscle fatigue,caused by doing sports,is a phenomenon of the decrease of the maximum voluntary contraction (MVC),which could be used in the fields of the prevention of occupational diseases in physiology or medicine and of the training of athletes in physical engineering.This paper adopted short-time Fourier transform to process the MMG,then gained the features of frequency domain,that is,mean power frequency (MPF) and median frequency (MDF),and finally investigated the relationship between these features and the degree of muscle fatigue.The subjects of this experiments were 9 healthy male volunteers who produced the muscle fatigue with constant force by performing 60% of MVC and simultaneously were recorded separately the mechanomyography (MMG) signals of flexor carpi radialis.By analyzing the parameters of the the frequency-domain gaining from the experiment,the results demonstrated that if the process of muscle fatigue were divide into 6 time segments,with the degree of muscle fatigue increasing,the average values of MPF and MDF——the two features of frequency-domain respectively presented the trend of an approximately linear decline at each time segment.During the 30 s of muscle fatigue,the declining range of the average values of MPF was 15.8% from the first to the sixth time segment,the declining range of the average values of MDF was 26.1% from the first to the sixth stage.The index of MPF and MDF based on short-time Fourier transform demonstrated high sensibility and stability to reflect muscle fatigue,suggesting the potential application of MPF and MDF as reference indices in evaluating static muscle fatigue.The method adopted in this paper and the results of this experiment provided the basis for the quantitative research of the degree of muscle fatigue by using MMG further in the future.