A complex terrain urban waterlogging simulation method based on drainage capacity analysis is proposed to address the problem of limited accuracy in simulating waterlogging in the main urban area of Guiyang City due to complex terrain and lack of pipeline data. The method is based on a fully distributed runoff simulation model, and constructs an urban waterlogging simulation framework that supports drainage output under complex terrain conditions. Based on the random forest algorithm, a bidirectional prediction model of drainage capacity and water depth is constructed, and historical disaster cases combined with precipitation data are used to predict the waterlogging process in Guiyang City. A flood simulation experiment was conducted on June 29,2024, and the results showed that 12 out of 16 historical flooding points were accurately simulated, and the model simulation accuracy met the practical requirements.