Abstract: Risk controlling measures reduce the losses caused by debris flow. Concerning the subjects of geology, engineering, sociology and economics, there are few case studies on debris flow from the aspects of the risk analysis, the risk quantitative assessment, the risk allowable identification, the risk mitigation measures selection, the monitoring and early warning engineering design and the cost-benefit analysis, etc. This paper takes the debris flow in Chengbei Gully of Jixian County, Shanxi Province as an example, using the Lidar technology to obtain the high-precision topographic data of the watershed and various parameters of the debris flow through field investigation, field tests and calculations. The FLO-2D numerical simulation software was used to divide the danger zones of the debris flow, delineating the threat range to obtain the vulnerability value, and then calculating quantitatively the risk value. When the allowable risk standard judges the risk as "unacceptable", risk controlling measures should be taken to intervene it. The total cost and the total benefit of various measures have been budgeted. According to the principles and methods of cost-benefit analysis, the net present value is determined to be RMB 5.08 million. The implementation of risk mitigation measures has economic benefits, providing references for the decision-making by the government and the public.