The 9 years gravity informations measured from 1991 to 1999 in Lanzhou-Wudu-Tianshui area are analyzed and compared. The relationship of gravity with the Yongdeng M_S5.8 earthquake on July 22, 1995 and Tanchang M_S3.9 earthquake on Nov. 18, 1998 is discussed by considering geologic structures. The results show that there were obvious gravity changes near the epicenters before and after the two earthquakes.