This paper analyzes the causes of cutting slope collapse in the excavation process. Factors causing the side slope stability failure are many and mainly geological, natural and engineering factors. With reference to the engineering practices of Lanzhou-Chongqing railway, the collapse at DK53 is analyzed with the conclusion that it is the internal unstable structure plane, the ground water seepage and the extraction of excavation that lead to the overall deterioration of stability of the slope and the collapse. In view of the above, comprehensive measures are put forward for foundation reinforcement, slope consolidation with drainage and anti-slide pile, which are proved very effective.