Abstract: We have analyzed the evolutional process of precursors, including observational data of leveling， GPS, gravity, deformation at fixed observ ational sites, mobile geodetic deformation and ground strain beforeand after the Zhangbei Ms 6. 1 earthquake. The results indicate that the deep-seated major fault plays a controlling and transferring role for the background field, and the epicentral region is situated at the relatively quiet region in recent years， which has experienced violent crustal movement. The closed coordination of background field with dynamic process of precursory anomaly is a key to the correct seismic situation determination. The new development of precursory anomaly after the earthquakeis of great significance in postseismic trend prediction.

Key words: Ground deformation, Precursory anomaly, Evolution characteristics, Zhang bei Earthquake