Abstract: Acoustic emission tests of uniaxial compression of different sizes of bump-prone coal samples were carried out by using rock mechanics testing machine and AMSY-6 launch signal acquisition system.With the aid of the G-R Relation in seismology,the dynamic evolution law of acoustic emission amplitude with time was dis cussed.The test results show that the b-value calculated by the cumulative frequency and the differential frequency can obtain similar rules,When the data amount is s mall,the cumulative frequency can be used preferentially.When the data volume is large,the differential frequency can be used preferentially.The b-value can be used to characterize the coal body failure process of acoustic emission,can be divided into b-value changes three stages: the initial downward stage,the unsteady transition sta ge and the linear decline phase,which can be attributed to the mode of "degression-undulating-descent' ,the three stages correspond to each stage of the stress-strain C urve.The acoustic emission trends of different sizes of coal and rock are different.With the increase of the size of e test piece,the b-value change tends to be unstable i n the early stage,and it shows a high consistency after entering the plastic stage,and the size effect of the precursor characteristics of steady damage is not obvious.Th e b-value of acoustic emission was reduced to the lowest point before the failure of coal body,and the b-value decreased in the peak stress range of 0.80 ~ 0.85,so the continuous decline phase of the b-value of the plastic stage is regarded as a precursor feature of coal and rock instability failure.