Abstract: With quite developed river network and convenient channels to the ocean, it is an effective way to use seawater as landscape water to improve water environment in Tianjin beachfront. A two-dimension cross-section numerical model for variable density groundwater and solute transport was adopted to analyze the degree and range of groundwater contamination caused by different seawater levels in the channels. The concealed piping for fresh water injecting moreover. And the control effect of groundwater contamination using the closed drainage for fresh water injecting in the channel bed was discussed. Result shows that salinity diffusion of channel coastal is obvious at high water level, and the salinity diffusion is controled at low water level. At low water level with closed drainage the salinity diffusion only occurs in the channel bed rather than in the channel coastal.