Based on the FVCOM model,a hydrodynamic numerical model is established in this paper,and the velocity changes of the enclosure gap under different gate widths and different tide levels are studied.The results show that:1) The tidal direction of the closure gap area is perpendicular to the entrance direction,the flow velocity during the high tide period is large,and the flow velocity during the low tide period is small.The aggregation effect at the end of closure gap leads to the maximum flow velocity appearing at about 20 m away from the end of closure gap on both sides,while the velocity is smaller in the middle.2) The protection period for the width of the closure gap in this project should be 200 m to 250 m,and the closure period should be 100 m to 150 m.During the protection period,attention should be paid to the erosion situation in the area near the ends of both sides of the closure gap,and the closure period should be selected during the low tide period.In summary,the width of the closure gap has a significant effect on the surrounding flow velocity.In this paper,the characteristics of the flow velocity of the closure gap under different working conditions are summarized,the recommended value for the width of the closure gap is given according to the numerical simulation results,and a reasonable time for the closure period is provided through data analysis.The research results can provide reference for similar engineering design and construction.