Abstract: In order to study the motion law of salt water when the levees break with storm surge in the delta estuary, one-dimensional and two-dimensional coupled salinity numerical models are developed to simulate the salt water movement when the levees break with storm surge. The impact of buildings in flood plains on the salt water movement and the gradient development process of the dyke breach are considered. The water levels and salinity calculated by the river networks model are tested with the measured data of multiple survey stations in 2008. The model is applied to simulate the salt water movement of an offshore dyke on the Pearl River Delta when the levees break with storm surge, and the maximum salinity isosurface diagram is mapped. The results show that the salinity of levee-breach flood in most of the breaches is over 4psu. Therefore, the impact of the high salinity ponding of levee breaches flood cannot be ignored. By comparing the drainage salinity calculated in the cases of "levee breaches" and "non-levee breaches", it is found that the levee breaches shunt of upstream enhances the storage capacity of tidal water, increases the flood tidal volume, raises the trace-back risk of salt water intrusion of downstream river network and weakens the suppressing effect of the upstream flow on salt water intrusion.