On 8 August 2017, an Ms 7.0 earthquake occurred on a buried fault extending to the north of the Huya fault. Based on the coseismic deformation field obtained from Interferometric Synthetic Aperture Radar (InSAR) data and a series of finite fault model tests, we proposed a brand new two-fault model composed of a main fault and a secondary fault as the optimal model for the Jiuzhaigou earthquake, in which the secondary fault is at a large obtuse angle to the northern end of the main fault plane. Results show that the slip distribution is dominated by sinistral slip, with a significant shallow slip deficit. The main fault consists of two asperities, which is bounded by an aftershock gap may representing a barrier. In addition, we find that most of the aftershocks were located down-dip of the high-slip areas and laid in stress shadows. We deduce that the aftershocks may be controlled by the background tectonic stress field, and may be related to the velocity-strengthening zones.