In this paper, the source spectral parameters of 183 ML≥2.5 earthquakes from January 2010 to June 2014 in southeastern Gansu were calculated by using the seismic waveform in the regional seismic network of Gansu Province. The variation characteristics of the ratio of P-wave corner frequency to S-wave and the ratio of P-wave long-period spectral level to S-wave before and after the Minxian M_S .6 earthquake on July 22, 2013 were analyzed, as well as the change of wave velocity ratio. The results indicate that: (1) The average value of corner frequency ratio is about 1.32, and the average value of wave velocity ratio calculated from the long-period spectral level ratio is about 1.55, higher than the former. (2) The time variation trends of the wave velocity ratios obtained by the two source spectral parameters are basically the same: “obvious rise-decline-sharp decline before the earthquake-slow recovery after the earthquake”; (3) The spatial distribution of wave velocity ratios are basically the same: low value anomalies appeared near the epicenter of Minxian earthquake before the earthquake, and the wave velocity ratio near the epicenter rebounded after the main shock.