Using P and S wave arrivals of local and near earthquakes,the crustal structures' of 7 subregions in Gansu were.inverted. The results show that:(1)vertical heterogeneity of velocity for Hexi region is greater than that for Hedong region, and those of focal regions of Haiyuan and Gulang MS events are greater than those for other regions,but horizontal heterogeneity is contrary. Vertical and horizontal inhomogeneity of upper crust(bounded at about 19 km depth) is greater than that of middle and lower crust;(2) velocity along the northeast edge of the Qinghai-Xizang block decreases along SSW-NNE direction in a regularly manner for upper and middle crust(bounded at about 30 km depth),but increases for lower crust; (3)horizontal inhomogeneity is characterized by outstanding lower velocity zone,which strikes along Qilian fracture system of SSE direction up to near Lanzhou, then extends southward to Zhouqu-Wudu,in middle section crosses lower velocity zone of the north edge fracture in western Qinling, but higher velocity areas locate mainly in north of Jiayuguanyumen, near Jingtai and south of Lanzhou etc.; (4) moderate and greater earthquakes occurred in not only lower velocity zones,but also higher velocity and other areas. The focal velocity of the two M8 events mentioned above is the lowest in middle crust of studied region. Thus,future strong earthquake possibly will occur near Lanzhou and in Zhangye-Minle region.