The stability of rock slope is mainly controlled by the discontinuous structural faces, so the continuum-based analysis method of slope stability is not suitable to evaluate the rock slope. To this end, by introducing the strength reduction theory into the DDA method, a discontinuous method evaluating the stability of rock slope is proposed. In addition, the strength reduction strategy and the basis for determining the safety factor are given. Then, the safety factors of a single block sliding on a inclined plane and multiple blocks sliding on a circular surface are calculated and compared with the theoretical values and the slice method results, respectively. The good agreement indicates the accuracy and validity of the proposed method. Taking the rock slope of the road in the site of Luoning pumped storage power station in Henan Province as an example, the deformation evolution process and displacement evolution law of slope under different reduction coefficients are analyzed based on the proposed method, and the safety factor of slope is determined. The results showed that under the influence of rainfall and blasting excavation disturbance, the slope failure first occurs at the foot of the slope, and then gradually develops to the top of the slope, which is consistent with the field investigation and monitoring results.The proposed method can provide a new research approach for the stability evaluation of complex rock slope.