In response to the difficulty in obtaining rock mass parameters and the instability of steep slopes in open-pit mines, Taking the high and steep slope of Panzhihua open pit mine as the research object. Non-contact unmanned aerial vehicle photogrammetry technology was employed to obtain the three-dimensional model of the study area, and the distribution of structural planes was statistically analyzed. Combined with rock mechanics test data, adopting the Engineering Rock Mass Classification Standard (GB/T 50218—2014) for rock mass quality classification, and the recommended values of strength mechanical parameters of the slope rock mass were given. Based on this, the dynamic evolution characteristics of slope stability in the mining area were analyzed by the finite element method under mining conditions, and the stability of the slope during the excavation process was evaluated. The results show that with the exploitation of the mining area, the slope near the mining face rebounds due to unloading, with a maximum displacement increment of 33.2 mm. The plastic zone mainly concentrates near the fault and the interface between the ore and the rock, with shear yielding as the main form. The factor of safety of the slope decreases gradually with the exploitation of the mining area until reaching the critical stability state. Anchors were used to reinforce the slope, and the stability before and after reinforcement was evaluated by the proportion of the plastic zone area, which evaluation coefficient α decreased from 0.4 before reinforcement to 0.05 after reinforcement, demonstrating the effectiveness of the reinforcement measures. The research results can provide reference for rock mass parameter estimation and stability evaluation of steep slopes in open-pit mines.