The rock mass encountered in actual geotechnical engineering usually undergoes long-term digenesis and geological tectonic action, and also subjected to repeated actions of loading and unloading repeatedly. This paper aims to study the influence of excavation unloading on the stability of a rocky slope, and the slope excavation process of Jinping Grade I Hydroelectric Station was selected as a case, and the 2D finite element software PLAXIS was used to evaluate the effect for the slope stability of without considering unloading and considering unloading, including stress, safety factor, plastic deformation zone and slip surface of the slope. The results show that the slope excavation unloading has a significant influence on the stress, stability safety factor, plastic deformation zone and slip surface, the stability of slope with considering unloading is far less than without considering unloading significantly. Therefore, the numerical method used to simulate the excavation of rocky slopes should consider the effect of unloading fully to service the engineering design and ensure the safety of engineering construction.