Protecting coastal area marine environments from pollution is critical to ensure sustainable development. However, the hydrodynamic and water environmental characteristics of many coastal waters are poorly understood. Furthermore, the levels of pollutants loading into coastal waters are rarely quantified. In this study, a hydrodynamic and pollutant transport model (based on MIKE 21 modules) was established in Qinhuangdao coastal waters, China. The simulated hydrodynamics and water quality parameters were highly congruent with measured values, exhibiting error levels below 20%. In Qinhuangdao coastal waters, the seawater flows primarily from southwest to northeast along the coast, with velocities in the range 0–0.4 m/s and 0–0.3 m/s during flood and ebb tides, respectively. Results from this study indicated that these waters were characterized by a weak tidal current, with mean velocities varying in the range 0–0.5 m/s. The chemical oxygen demand (COD) concentration of the coastal waters was in the range 0.1–3.7 mg/L, and the COD pollutants were diffused approximately 3–10 km off the coastline. The water environment carrying capacity (WECC) at each point source was also calculated based on the response coefficients; further, WECC in Qinhuangdao coastal waters was calculated at 544.01 t/a and 1088.02 t/a under two Chinese water quality levels (levels I and II), respectively. The results provided specific valuable information for controlling pollutants from rivers into coastal waters and managing the Qinhuangdao coastal waters environment.