Abstract: The stability analysis of unstable rock mass in steep slope has always been the focus of researchers' interests. The traditional stability evaluation methods are based on qualitative analysis. The numerical simulation can accurately establish complex 3D geological model rapidly and analyze the stability of unstable rock mass quantitatively, with the support of reverse engineering modeling method. Based on the geological survey results, the paper scans the potential geological hazard points of Shenlong Waterfall Slope in Shenxianju, and gives a model reconstruction of the scanned data through the Geomagic Studio software. It uses Hypermesh to process the surface model, simultaneously calculates the obtained grid data and carries out the finite difference numerical simulation calculation with FLAC^3D. According to the results, the maximum tensile stress of the unstable rock mass is close to its tensile strength. It is likely that rockslide-rockfall can occur. In addition, the paper uses the FISH language in FLAC^3D to calculate the failure probability of the unstable rock mass based on the proportion of the number of plastic failure elements in discontinuities. The results show that the probability of failure is more than 20%. The results correspond well with the results of the geological survey and numerical analysis. The paper also forecasts the failure of the unstable rock mass, and proposes the preventive and control measures. The paper can provide the theoretical basis and have certain reference value for the disaster prevention works of the local tourism administrative department.