Rock bolt crane girder is a structure form which is widely used in the underground powerhouse of hydropower station. It makes reinforced concrete anchored in the underground powerhouse rock using anchor rod, and makes the reinforced concrete, anchor rod and surrounding rock work together to resist the load. Stability has been a common problem in the realm of engineered construction. This article will analysis the stability of the rock bolt crane girder in a underground powerhouse of hydropower station by using the traditional rigid body limit equilibrium method and the finite element method, and give several destroying forms. The results show that the rigid body limit equilibrium method is flawed, need to be corrected; In overload cases, the contact surface of girder and rock crack, it turns the damage to the bottom O point at the end; When it is simulated by the strength storage method, the crane girder's shear yield slips the damage along the base.