Estimation of roughness parameter is a key to one dimensional hydrodynamics numerical simulation.For a mountainous river,because of the great variation of river morphology along flow route,the local energy loss has a great impact on hydrodynamics.According to the hydraulic feature of mountainous rivers,this paper proposes a method to estimate a synthetic roughness that gives a good expression of friction loss and local resistance in the sub-segment.To examine the proposed method,a simulation case on open channel is used and a good result is obtained.The proposed method simplifies the sub-segment demarcation and normalizes the estimation of roughness parameter.