Abstract: In this paper, the repeatedly measured data of gravity in Northern Qilian Hexi area are analyzed; evolution of gravity field and its relation to strong earthquakes is studied.from the view point of dynamics.7 earthquakes M_s≥5. 0 occurred in and around the area during the measurement period are certainly reflected by mobile gravity， and are partly predicted to a certain extent. It is found that the anomaly patern, amplitude and lasting time of gravity variation are well correlated with earthquakes; the gravity field dynamic pictures clearly show the evolutional process of gravity variation from inhomogeneous state before the earthquake to recovering after earthquake.

Key words: Gravity anomaly，Earthquake precursor, Evolution of gravity field, Northern Qilian-Hexi area