Aiming at the characteristics of multi-breach of bank in pearl river delta basin under great flood,this paper established a multi-breach one-dimensional and two-dimensional coupling mathematical model in the pearl river delta by taking one-dimensional and two-dimensional unsteady flow basic control equation as theory base.It used weir flow equation to realize the real-time interaction between the river network and the flood control protection zone in coupling position.This model took controlled dike burst way of changeable width to set up parameters,and used local terrain correction's method to deal with the effect of guiding and flowing of water of roads and water culvert in flood control protection zone. It carried out optimization treatment of terrain by setting roughness region and increasing local roughness, applied dry and wet judgment theory to optimize moving border.The verified model was applied to simulate the multi-breach flood occurred at Jiangxinlianwei flood protection zone.The paper analyzed the big difference between the submerge result of flood caused by single-breach flood and that by multi-breach flood.The result can provide important reference for the risk evaluation of multi-breach flood in the pearl river delta and other similar areas.