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Abstract.Over the past few decades, there has been large-scale land reclamation in the Hangzhou Bay, which inevitably has affected the hydrodynamics in the bay. In this study we set up a 2D hydrodynamic model based on Mike21 Model to investigate the changes of hydrodynamic in the Hangzhou Bay due to large-scale reclamation. This model is well validated with the measured data.After that the validated model is run with different coastlines in 1960s and 1985 respectively. The simulated results indicate that after the large-scale reclamation project of the Hangzhou Bay, 1): The high tide level increases and low tide level decreases, which lead to the tidal difference increase; 2): the time of the ebb turning to flood at Zhapu and HZB1 are both ahead, and the flow direction has no significant change out of the bay; 3) The flow magnitude reduces from the mouth of the bay to the inside, and the extent of reduction increases with the speed reaching 1 m/s as it to Haiyan.