In the conversion of surface raining to underground operation, the rock of slope is still a serious problem, und will cause harm if neglected, as demonstrated by some instances given in this paper. Based on the study on the slope stability in the conversion of surface mining to underground, operation, in Zheyaoshan copper mine operated by Baiying Co., the analysis of the factors affecting slope stability is made. And it is pointed out that the large scale slipping of the complete slope is too impossible in the initial stage of the underground operation, while the limited local slipping does no harm to mining operation. However, the emphasis should be placed on monitoring and measuring, and the prevention and prediction of sudden slipping should be done well.