The problem of saltwater intrusion in the Pearl river delta is very serious especially in recent 20 years. The Pearl River network is complicated with hundreds of channels connected and 8 outlets in the downstream, which makes the hydraulics in the delta much more difficult to analyze. Numerical model is considered as the main method to study the saltwater intrusion because numerical simulation can reduce cost and time as well.To analyze the process of saltwater intrusion, we set up the model with a combined mesh style (triangular and quadrilateral) , which covers both the Pearl River network and the estuary, and finite volume method is applied to discrete the space. The result showes that the calculation values of tide level, flow velocity and salinity are consistent with the measured data, which proves that this model can be applied in real engineering.