Characteristic motion of wash load is different from bed material load. In the past lots of studies assumed the wash load is 70∼90% of total suspended sediment in the river because of lacking data. It is difficult to define the grain size and proportion of wash load accurately by using this assumption; so sediment discharge could not be estimated precisely. The purpose of this study is developing a relationship of proportion of wash load with the influential factors in river. The relationship formula of wash load associated with suspended load is established by using the multivariate regression analysis with data collected on lower Kaoping River, Taiwan during the typhoon flood events. The effect of proportion of wash load on river deposition-erosion is carried out by using a 1-D mobile-bed model. Different inflow sediment concentrations associated with general empirical method and relationship formula of wash load are compared It can be known that the bed change simulated by the relationship formula from the observed values is superior to the result from general empirical method. In summary, the relationship formula of wash load provides not only an innovation method, but also some the subsequent applications.