Abstract: A 3-D numerical model with inclined pressuare is developed to compute saltwater intrusion in large estuaries. Adopting the a-coordinate transformation in the control equation,the same grids in vertical coordinate direction are used to the local topograph. The model uses mode-splitting method for surface gravity waves (external mode) and internal gravity waves(internal mode). The external mode is sloved by the improved double-sweepimplicit finite difference method. The internal mode utilizes the Eulerian-Lagrangian method,improves the implicit-difference scheme for the vertical direction,and reduces numerical diffusion. The model raises the calculative accuracy and stability. The model has been tested by computing the saltwater intrusion in Changjiang estuary and the results shows the current and Salinity time-space distribution of computation is in agreement with the measured data.