Abstract: Flood returning to main channel leads to an increase in flood flow and water level, which must be considered in flood prevention and l embankment engineering design. Based on measured flood process and the terrain of the floodplain, a method is proposed to obtain the flood process returning to main channel by overflow process. Which is generalized according to the flood volume , the occurrence time, and the evolution characteristics of overflow. This method is applied in the June 1959 flood in Heyuan urban area. The results show that the flood process returning to main channel is sharper and thinner. The calculated peak flow at Heyuan Station is 7765 m3·s-1, which is 5.8% higher than the measured peak flow. And the peak occurs at 18: 00 on June 13th, which is 23 hours earlier than the measured time. It provides a reference for calculation of flood returning to main channel.