Since a long time of excavation, the slope in Yang-mountain of Suzhou Province became a high and steep slope which has 260m difference in height, on top of this slope there is a high risky cataclastic texture bedrock landslide. Based on geologic investigation of the landslide, combined with 3DEC numerical simulation, the paper gave a comprehensive analysis on formation precondition, evolution procedure, failure model and mechanism from the points of topographic feature, structure evolution history, lithology and external influence. It is shown that the free face in front of the landslide, weak quartz porphyry dike in front of the sliding zone, cataclastic rock structure formed by nappe structure are the main factors which control the formation and failure mode of the landslide.