For a tension-fracture rock mess as a specially geologically isolated body, the method to evaluate the stability of the kind of rock mass is still immature. With the tension-fracture rock mass of the right bank of some hydropower station as an example, the safety factors before and after regulation are calculated by the two-dimensional limiting equilibrium method, and then according to external deformation observed results, and the monitored data from the inclinometer and the sliding micrometer, the position of possible sliding face and the slide possibility are discussed in this paper. We come to the conclusion that the slippage of “ fracture zone ” is the main reason of the slope deformation and the slope mainly tends to be stable in the construction period.