Abstract: Based on Navier-Stokes equation,the model equation is deduced through a-coordinate transformation,then by selecting a series of the specific interpolation value function,using the combined method of the finite element and the difference,solution is obtained,the model is very suitable for calculating tide current in the sea area with complex bank boundaries or harbour engineering construction,which also can achieve densifying calculation in local or partial region and can reveal the space structure characteristics of the three-dimensional tide current with higher distinguishable rate,the model has many advantages such as being simple to application and saving calculation time.