This paper aims to the accuracy improvement of a two dimensional flood flow numerical model by applying easily obtained vegetation characteristics that can be considered to use for future river management. Despite former works in which the effect of vegetation was included in the determination of Manning's roughness coefficient, in the new model, the resistance of the vegetation is introduced by adopting the concept of the drag force to deal with the deformed situation of the vegetation under flood flows. The vegetation density was distinguished by different types of plants, i.e. trees, bushes, bamboos and annuals. The resistance of annuals depends on the flow rate, therefore, the deformation of plants is considered as a decreasing factor of the resistance. The model was checked to confirm its applicability by comparing the analysis to the water surface profile and flow characteristics of the flood flow in the Asahi River and found a good agreement with the results.