Abstract: Taking the 1979 M_W6.5 Imperial Valley earthquake as an example, we compared the three methods of pulse-like strong motion identification, that is, wavelet analysis, peak-point method （PPM） and zero velocity point method （ZVPM）. The identified peak values are similar, however, the identified pulse periods are slightly different. To analyze the mechanism of the velocity pulse, including the generation time, location, and the impact of asperity, we use the frequency-wavenumber Green’s function （FK method） to synthesize broadband ground motion. PPM is used to gradually identify the velocity pulses during the superposition of the sub-source ground motions. Analyzing the changes of the frequency components in sub-fault ground motion during the superposition process by using time-frequency analysis method and the impact of the spatial relationship between the asperity and the station on the pulse generation, preliminarily discuss the generation mechanism of the velocity pulse.