Using an improved ECOM model, designing an idealized strait and funnel-shape estuary, the impact of the estuarine funnel shape on the estuarine circulation and saltwater intrusion is studied. The saltwater intusion produces salinity front, there exists a land-ward density induced current under the salinity front, and the current speed at the upper layer obviously enhances due to mass continuty through the transverse section. There is a northward component of current at upper layer and a southward component of current at lower layer, this indicates that there exists transverse circulation. The salinity front induced by saltwater intrusion inclines northwestward horizontally that means the saltwater intrusion at the north coast of the estuary is stronger than at the south coast, and inclines toward upstream vertically that means the salwater intrusion at the lower layer is stronger than at upper layer. The higher salt water locates at the lower layer and near the north coast. The dynamic factors of saltwater intrusion are the tidal flood current, the land-ward density current and mixing. The Coriolis force makes the flood current deflect to the north coast, and the land-ward density current exists at the lower layer, those dynamic mechanism result in asymmetry distribution of salinity. The baroclinic pressure gradient force induced by the salinity distribution in transverse section directs the south coast and increases with the water depth, this results in the current at botton layer flows to the south coast. In order to keeping mass conservation, the divergence at bottom layer and north coast produces upwelling and rise of water level. This transverse distribution of water level makes the surface current flows northward, the above dynamic process induces a transverse circulation. The current divergence induced by the spreading width of funnel -shape estuary inner the mouth makes the current weaken and produces upwelling, the distance of land-ward flow of density current at bottom layer reduces,the salinity near the mouth increase, but the saltwater intrusion weakens; There exists obvious higher saltwater at the botton layer and south coast of the funnel-shape estuary; The vertical mixing enhances, and salinity tends to uniform vertically.