Based on the plan to build an artificial island in Dalian bay, under a variety of artificial islands in the combination of length and width conditions, and using MIKE21 flow model, we simulate the gulf flow field before and after the construction of the artificial island. Under the concept of the tidal level gap, we study the water exchange, pollutant dispersion and retention rate in the gulf, and evaluate the impact of the artificial island on the water environment in the gulf. Under different functional premises of the artificial island, and considering many factors of the artificial island and water environment, we put forward the recommendation for the artificial island.