Abstract: Based on repeated gravity observations data from 1996 to 2007 of the Longmenshan gravity network, we first carried out adjustment processing, removing of benchmark interference and impact of elevation changes. Then by using 3D inversion method to reflect underground density, we analyzed the characteristics of Longmenshan regional dynamic density in the depths of 25 km, 20 km and 15 km.The results show that in the Wenchuan earthquake inoculation process, regional density field showed obvious characteristics both in time and space distribution. From the point of time process, the density change trend ten years before the earthquake present periodic change: steady phase, dramatic stage, slowly reduce phase and slowly increase phase. The amount of density changes is from large to small, which shows that earthquake gestation has reached the final stage. From the point of space distribution, density change distribution has a tendency of “dispersionrelative concentration”, which shows that before the earthquake underground density field exit entropy decreasing. In addition, the density dramatic change region tends to lie in Longmenshan fult zone and the western Sichuan plateau. Besides, with the increase of depth, the trend of density change is more and more obvious. Through comparative analysis, the influence of density change on gravity is far more than height change.

Key words: Dynamic change of density, 3-D inversion, Wenchuan 8.0 earthquake, Longmenshan fault zone