Abstract: On August 8th 2017, a M_W6.5 earthquake struck Sichuan Province, China, resulting in significant loss of life and extensive property damage. The absence of significant surface rupture from field investigations made it challenging to identify the fault geometry and estimate the rupture evolution of this event. We applied a newly potency density tensor inversion which introduced the standard deviation of the smoothness constraints for five basis double-couple components by the weight of its each amplitude respectively to estimate the rupture process of this event. The slip distribution shows that large slip regions coincide with distribution of aftershocks, especially for the depth change in the southeast and northwest epicentre. Both aftershock and slip distribution show deeper depth in northwestern segment than that southeastern segment. The spatial distribution of potency density tensors showed different total focal mechanisms for the northwest and southeast area of the epicentre, indicating that the complex seismogenic fault of the main shock may be divided into two main segments and a secondary segment. The rupture process shows that the initial rupture occurred around the hypocentre in the first 2 s. Main rupture propagates to the up-dip part of the hypocentre while partial rupture propagates to down-dip part of the hypocentre within the southeastern segment of the seismogenic fault during 2-6 s. Then rupture jumps to the northwestern area of the hypocentre and propagates with in northwest segment during 6-10 s. In addition, moderate slip appears in the southeast edge of the fault plane from 5 s. High and low-velocity anomalies were identified around the hypocentre and in the northwestern and deeper parts of the hypocentre, respectively. We interpret that the brittle failure of rocks, caused by stress accumulation from middle-to-lower crustal flow and upwelling asthenosphere, may have contributed to the initiation of the 2017 Jiuzhaigou earthquake. Additionally, the deceleration and cessation of the event are inferred to be related to the fault geometry along the strike direction and the seismogenic environment at depth.