Abstract: River clogging is a natural disaster caused by landslide which results from earthquake, rainfall and other factors. Among the many losses caused by river clogging disaster, the loss of life is the most serious loss. In this paper, according to the disaster mechanism of life loss because of river clogging, the evaluation index system including risk population, warning time, understanding degree, lake level rising speed, elevation of risk population, submerged depth and other parameters, and the quantitative evaluation method of each parameter is established. At the same time, a bayesian network model, consisting of emergency evacuation network, submerged water depth network and life loss quantitative assessment network, is established through the interaction among various factors to assess the life loss of river weir, and the case of Niulan River weir is used to verify the rationality of the assessment method.