This paper aims to discuss the relation between basin characteristics and runoff model parameters. As a flood runoff model, kinematic wave model of overland flow type is examined by dealing with the data in the Shimokari natural hilly watershed of 1.3<km>^^^2, the 93% area of which is covered by bushes and bamboo groves. First, a standard watershed model is constructed by applying a stream network system, in which first order streams are defined by using the ratio of wide and length in the contour crenulation on a topological map. The lumped watershed models are based on both Strahler's and N_1 ordering systems. Second, the optimum parameters of overland flow model is identified for standard and lumped watershed models. And the estimating formulae for optimum model parameters have been proposed in relation to the contributing slope length in the ordered watershed modeL
Third，simplified runoff model of overland flow type omitted the calculation of channel flow is examined and the applicability is evaluated in relation of lumping the watershed model.