A lot of slopes will be formed in the process of engineering construction, and how to ensure the slope stability has become a very key field and common concern to geotechnical engineering. Taking the slope of a open pit mine as an example, the slope stability at original state is analyzed firstly, and then, the optimal control measure and the slope stability trend during the treatment are also researched. The results show that at the original state, the slope stability is worse, and a large contiguous plastic regions will occure on the slope. After comparing to some methods, local unloading is identified as the optimal control measure. When unloading works are carried out and finished, the slope will be in a steady state, and the slope safety factor will up to 1.46, it satisfy engineering requirement.