It's needed to consider the effect of tidal current in order to numerically simulate the circulation realisically in a shallow sea, because the tidal mixing and tide-induced residual current have an important effect on the circulation. It's needed to set the current speed for the open boundary condition in stead of set the water level in order to balance of water volume flowing in and out the calculated domain. First, we verify the consistent of the tide and tidal current in the calculated domain in the case of open boundary condition with tidal level and tidal current. Then we consider the composition of the residual current and tidal current. It's necessary to verify numerically that whether we can give out the open boundary condition with the composition of residual current and tidal current simultaneously. Applied the ECOM, the numerical experiment with the tidal current open boundary codition shows that results are consistent with the tidal level open boundary condition by designing an idealized bay. It is successful to simulate the distribution of residual current in the case of considering the residual current and tidal current at the open boundary simultaneously. The conclusion in this paper can be referenced for the numerical calculation of current in the case of composition of residual current and tidal current.