Affected by human activities and other natural factors,the lower reach below Chaizhuang of the Fenhe River has been silted continuously,the capacity of water transferring has been decreased in a large scale,and a great change has been found with the flood characteristics in the river reach,which lead to failure of normal flood forecasting.A method of flood routing in normal river channel and flood channel respectively is proposed in this paper,the concentration feature of the river reach is reflected,the result is proposed in this paper,the concentration feature of the river reach is reflected,the result is satisfactory,the difficulty of flood forecasting in the reach is resolved,and it is worthy to be spread.