Abstract: Landslide dams are formed by the collapse, landslide, mudslide and other unstable bodies. Due to the short lifespan of the dam and the long affected basin, the existing methods are difficult to assessment the dynamic risk of entire disaster evolution process across the basin. In this paper, a dynamic risk analysis method was proposed based on geometric parameters of the dam, the three-dimensional topographic information of the river and the population distribution data. Besides, the dynamic risk analysis of the Tangjiashan landslide dam was carried out, and quantitative risk value of the downstream was obtained. The results show that the risk level of the risk zone is generally negatively correlated with the distance, the closer the dam site is,the higher the risk is. The dynamic evolution of the risk is usually delayed, when the risk zone near the dam site receives the risk, there is still no risk in the distant area; while the risks in the nearby begin to dissipate, the risks in the distant areas increase. The analysis results are in good agreement with the actual risk situation of the Tangjiashan landslide dam, which has important reference value for later risk management.