Abstract: The two-dimensional tidal current numerical model was used to predict the environmental impact of 4 
drains and simulated under the condition of normal discharging and accident dischaige. Combined the impacts with 
factors of water depth，dynamic conditions and otfiers the optimal effluent discharge points for the marine sewage 
discharge were selected in Dongjiakou port. The results show that current in the area studied is mainly of semi-diurnal and the movement type places alternating current firet, rotational flow the second and the maximum velocity of 
fluctuation directs to SW—NE. Generally, sea area in the south of connection between western bulwark and LNG wfarf has a better hydraulic condition. As result, the outlet P4 is optimal due to active hydrodynamic condition with 
suitable water depth and advantages of pollutant dilution and diffusion. Besides , it impacts little on Rizhao seawater 
and the Rizhao Codenterate antiquate Germplasm Reserve in case of accident discharge. At the same time, consid
ered that the seawater around P4 follows tfie Grade III of Water Quality Standards, the areas around the outlet with 
water quality not better than Grade III would be smaller than 0.742 km2 and the length of North-Southward diffusion 
would be less than 0.34km by the simulation. As the diffusion direction is consistent with die current, the condition 
is favor for pollutant dilutions and dispeisions. The numerical simulation reflects objectively the concentration changes and pollutant movements and it is a fundamental Support for the marine environmental management planning and 
total amount control of effluent discharge.