Okinawa region has been suffering from severe red soil runoff which is caused by heavy rainfall and overland flow. The soil particle is very fine and will not sink once the soil is eroded and involved into water flow. The muddy water containing red soil particles pollutes the shores and coasts, and it gives heavy damage to ecosystems of the sea, farming and tourism. In this study we developed a distributed red soil runoff model which describes the erosion process of plane soil surface due to overland flow on the basis of a kinematic wave flow model and a digital topographic model. The erosion of surface soil is assumed to occur at a point where overland flow occurs. The rate of erosion is calculated by using the friction velocity at the point, which is determined from water depth of overland flow. The model was applied to Taiho River basin (24 km²), which is located at the north part of Okinawa main island. The results of simulations showed good agreements with observations, while the model needs further improvements.