Under extreme storms, multiple hazards such as landslides, debris flows and floods may occur simultaneously. This study conducted numerical simulation of rainfall-induced hazard processes, aiming at deciphering the main weaknesses of an urban watershed exposed to slope failures, floods and debris flows. Under storms of 44%, 65% and 85% of the 24-h probable maximum precipitation, 0.5-1.7% of the natural terrain of the study area can lose stability, and 18.2-21.1% of the urban area may be flooded. The travel distance of debris flows can reach 833 m. The hazards of slope failure, flood and debris flow could occur in a same site over a relatively short time interval. Therefore, hazard interactions are very likely to happen, especially in the flow channels where will be affected by all the three hazards.