Present methods for stability analysis of underwater slopes are mostly confined to laboratory experiments and limit equilibrium method. This paper is based on strength reduction method, considering the deformation parameters of rock mass to discuss the stability of underwater slopes. Comparing the consequences, the sliding planes and safety factors agreed well with the result of limit equilibrium method. The applicability of strength reduction method for underwater slopes stability was well proved. When analyzing after changing the water depth, it was showed that there are more erosion effect induced and reduction for the parameters of rock mass, but little influence on the safety factor of underwater slopes.