This paper determines and analyses crust medium quality factor, Q value, in the eastern Gansu area and Xiji-Haiyuan-Guyuan area of Ningxia, assuming that crust medium is visco-elastie. The mean Q value calculated by power spectrum of the direct P and S wave is 126. The mean Q value is 58 in low value area. The Q values are high in Haiyuan and Lixian area, the mean Q value is 194 and 957 respectively. The Q value is low in Diebu area, its mean Q value is 48. These high and low Q values occurred before and after main earthquake.