Abstract: A 2-D hydrodynamic mathematic model which shows characteristics of furcation and conflux flow on slopes is developed.The flood transmission in the furcating flow area of Dasha River,Henan Province,before and after the construction of the main canal of the South-to-North Water Transfer Project is numerically simulated.The improved scheme according to the numerical calculation results can effectively reduce the local submergence in the left bank of the main canal.