Abstract: A hydrodynamic and pollutant transport model of Beidaihe coastal water is first setup by the utilization of Mike 21 software, and the model includes the Renzaohe River, the Yanghe River and the Daihe River. Then the model is well verified by measured data of tidal current and concentration of Chemical Oxygen Demand (COD). Finally, the effects of different schemes on reduction of river pollution source strength are compared and analyzed through numerical simulation results. Numerical results indicate that the COD environmental capacities in coastal areas around the Renzaohe River, the Yanghe River and the Daihe River are 375.076 t, 346.803 t and 309.833 t respectively in August, 2013, and required reduction amounts of COD source strength from high to low are the Yanghe River, the Renzaohe River and the Daihe River. The areas where the COD concentration is over the standard value are different even though there are the same reduction ratio of pollution source strength in three rivers, i.e., the effectiveness of pollution reduction in the Daihe River due to weak water exchange capacity is higher than that in the Yanghe River and the Renzaohe River. With the increase of reduction ratio of river pollution source strength, exceed standard area decreases, but its decrease rate becomes low.