Abstract: This paper firstly introduces the gravity anomaly separation methods, then adopts the preferential filtering method to analyze the characteristic of gravity field in the Lushan earthquake zone and its adjacent areas, so as to shed some lights on the tectonic background of the earthquake in the subsurface. The preliminary understandings are: ① A remarkable gravity gradient zone (GGZ) trending NE presents along the Longmenshan faults zone, and to the south of Tianquan county it is splitted into two branches; ② The epicenter of this earthquake is near the crotch of the GGZ, and the aftershocks with M_S≥3.0 strike NE, which is consistent with the strike of the GGZ. All the results indicate that the generation of this earthquake is closely related to the deep structure and tectonic activities beneath the GGZ. There is a large difference between shallow structures and deep ones in Lushan earthquake zone, in addition, complex structures as well as poor coupling between shallow and deep part of the crust also exist, implying the generation of Lushan earthquake was controlled by both shallow and deep structures.