Abstract From the repeted gravimetry data of Dianxi Experimental Field from 2005 to 2009, local differential and cumulate gravity change pictures have been obtained. The study results from the data are as follows.1)The dynamic evolvement pictures of gravity field can generally reflect the movement state of the crustal substance before earthquake. Shortterm local effect is obviously reflected by the differential dynamic change, while local tectonic movement and fault structure effect by the cumulate dynamic change. 2)A positive and negative transitional gravity gradient zone across the epicenter along almost northsouth direction appeared two years before the earthquake, and a symmetrical fourquadrant distribution of the gravity change appeared too around the epicenter half year before the earthquake. They were the prominent gravity precursor marks of the Yaoan earthquake. 3)Durative positive gravity change appeared in the west to the epicenter three years before the earthquake. It was helpfull for energy accumulation. 4)The relatively highlow fourquadrant distribution picture may reflect that there exist a shearing stress. So we put forward a ‘lock in shearing force mode’ for the precursor model.
