To ensure the safety of soil slopes in open-pit mines and enhance their instability resistance under extreme rainfall conditions, this study conducts an empirical analysis at an iron ore mine in Guangdong. Innovatively integrating numerical simulation with engineering practice, it proposes a collaborative treatment strategy combining slide-resistant piles with a surface drainage system based on slope reshaping. A 3D geological model was constructed using the MIDAS platform, and multi-scheme comparative verification determined that the optimal pile parameter combination increases the slope safety factor by 5.3%, while effectively regulating the displacement field and stress distribution of the slope body. The supporting drainage system employs rectangular intercepting ditches along roads and trapezoidal drainage ditches on benches, with hydraulic calculations confirming its capacity to handle rainstorms with a 20-year recurrence interval. Engineering practice demonstrates that through the synergistic effect of structural reinforcement and waterproof drainage, this solution significantly improves slope stability while delivering sound economic benefits, providing a technical reference for similar mine geological hazard prevention in South China.