Abstract: The analysis has been made for the repetition measurement data (in Zhagngjiakou area in the west of Beijing)of the No.24 phase from 1987 to 1988 of the north circuit of railway-mobile gravity survey net in North China.The gravity a nomalous variations in the developing process of the Huaian M4.5 earthquake occurred on May 25,1997 and the Zhangbei M6.2 earthquake on January10,1998 have been discussed.The research shows that the variational characteristics of time and space distribution of the gravity field clearly reflected the evolution process from the nonhomogenous state of earthquake preparation to earthquake occurrence.