Abstract: The tidal river reach is an area where the river and the ocean interact and influence each other. The change of water level in this area is related not only to the discharge flood of river, but also to the nearshore tidal phenomenon. In many areas the basic hydrological data is very scarce and even no complete hydrological data can be found in the entire drainage basin of some rivers. As hydrological data for wading projects are lack in the tidal river reaches, the Java Coastal Power Plant in Indonesia is taken as an example to introduce the calculation principle of HEC-RAS (Hydrologlic Engineering Center’s River Analysis System). And the HEC-RAS model is used for calculating under different working conditions the water surface profiles of the tidal river reaches where the project is located. Combining with the regional hydrological conditions and using a reasonable model scale, the calculated results are verified by a physical model test carried out by superimposing the river flood peak and the high tide level encountered once in 100-year in the sea. The results show that by determining reasonably the upstream and downstream hydrological boundary conditions and the model parameters, the simulated results of the water surface profiles of the tidal river reaches are reliable. This can provide reliable hydrological parameters for engineering design.