According to the tidal current characteristics of drainage and receiving water in LNG project and the typical hydrological conditions of design in different seasons, the paper used a two-dimensional hydrodynamic model to simulate the tidal current field of water receiving residual chlorine in cold water discharge in radial sand ridge group of shallow sea area of Jiangsu maritime space. As the hydrodynamic conditions in the simulation of cold water mobility and transfer of residual chlorine in the reception area of time and space distribution characteristics,it established a two dimensional model of the transport and diffusion for the residual chlorine to predict the receiving waters residual chlorine concentration distribution and analyze its environmental impact in considering the residual chlorine in water body of attenuation effect at the same time. Finally, the scope of influence caused by the chlorine water drainage in the chlorine water's sphere was analyzed quantitatively according to the chronic toxicity threshold line of residual chlorine. Results show that the residual chlorine in cold drainage of LNG project has less impact on the water environment in offshore area.