Abstract: Urban construction needs to carry out urban drainage planning according to local conditions, climatic conditions, rainfall characteristics, underlaying surface conditions, and conduct rainstorm flood management to achieve the purpose of reducing rainwater runoff, regulating runoff peak and reducing the risk of waterlogging. In this paper, based on the data collection and sub-division of study area, the characteristics of rainfall and runoff in the mountainous area of Tenom District in Malaysia were analyzed. Meanwhile, to identify drainage problems, a 2-D hydraulic model was set up to assess performance of the existing stormwater drainage system. The capacity of drainage system and flood loss under different design schemes are evaluated, and the overall planning scheme of future drainage system is put forward to meet the demand of future social and economic development of Tenom District.