Abstract: The theoretical seismograms were calculated with transfer matrix of generalized reflection and transmission coefficients.Through comparing them with actual P waveforms, and using Fast-simulated-annealing-algorithm to search the best velocity model, we obtained the P wave velocity structures beneath 13 digital seismic stations in Shaanxi province.These stations distributed in three tectonic regions, which is Qinling orogenic belt, Weihe graben and Ordos block respectively.The results of inversion show that the velocity structure beneath each tectonic unit is different obviously from the others, showing its own tectonic characteristics respectively.In Qinling orogenic belt, there is a high velocity layer from upper crust to the surface, and there are several low velocity layers in mid and lower crust, which may be related to rock dehydration and tectonic slipping.In Weihe graben, high and low velocity layer occurs alternately in upper and mid crust, which reflects the effect of faulting in shallow crust.In Ordos block, part stations keep steadily uniform velocity structure, representing the steady development of ancient stratum, but affected by post reconstruction, low velocity layers increase under some stations.Since the stations with large velocity change between some layers are mainly distributed in the south and west of Weihe graben, and the main stress direction from focal mechanism is nearly in east-west direction, it is concluded that the faulting at the north boundary of Qinling and the compression later from Qinghai-Tibet plateau are the main factors in the formation and development of Weihe graben.Finally, the relationship between velocity structure and strong earthquakes, spatial distribution of earthquakes, and different tectonic evolution were discussed.