The Cold drainage of LNG project have an impact on the water environment in the sea area. Based on the Shenzhen LNG project, the 3D hydrodynamic residual chlorine model (MIKE3) was used to calculate the migration law of residual chlorine in seawater, and the influence of cold drainage of Shenzhen LNG project on the water environment of Dapeng Bay was analyzed. The calculated tidal level and tidal current at different water depths are verified with the measured data, which confirms the reliability of the established 3D hydrodynamic model. On this basis, the horizontal and vertical three-dimensional spatial distribution characteristics of residual chlorine concentration in the receiving sea area under typical spring and neap tide conditions, as well as the interaction of multiple emission sources were calculated. The results show that the residual chlorine has no direct impact on the sensitive targets of the surrounding water environment and the water intake of other projects.