Abstract: Aiming at the creep deformation and bedding instability of the water-bearing soft rock slope in open pit mine, in order to determine the reasonable slope angle, taking the southern slope of the Dongming open-pit mine as the research object, on the basis of engineering geological prospecting and mechanical experiment ,the deformation and failure characteristics of bedding soft rock slope under the action of groundwater are studied by using FLAC3D,then the limit equilibrium method is used to compare and analyze the influence degree of groundwater on slope stability, finally, the slope Angle is optimized by the finite element strength reduction method. The results show that, the influence of groundwater on the stability of the southern slope of Dongming open-pit mine is obvious,the stability coefficient of the position of the soft rock surface is 20.73% lower than that under normal conditions, taking the above factors into consideration, the ultimate stability Angle of the south slope is determined to be 22°.The optimization design method of slope parameters on the basis of limit equilibrium analysis and finite element strength reduction could scientific and reliable determine the limit stable slope angle .