Abstract: An improved 3D numerical model ECOM-si, coupled with the drift and diffusion module of oil film, was adopted to simulate the thickness and trace of the oil film after an oil spill accident (100 tons leakage) is occurred at the main pier of the highway bridge in the Yalu River. The model results show that the oil film reaches the water intakes of Sidaogou and Dandong Paper Mill at 0.9 h and 1.5 h after the oil spill, experiencing duration of 0.6 h and 1.7 h in summer, respectively. The oil film reaches the two places at 1.2 h and 1.7 h after the oil spill, experiencing duration of 0.6 h and 2.5 h in winter, respectively. No matter in summer or in winter, the oil film will not reach the water intake of Yanwo. Although the river discharge in summer is much larger than the one in winter, the oil film drifts upstream farther in summer than in winter during flood current. The numerical experiment results show that the stronger flood current in summer is only the second reason for the pheonomena, while the wind is its principal reason. The orientation of the river is north-west near upstream the bridge which results in the oil film blocked by the northwest wind in winter, and is almost north-south farer upstream the bridge which results in the oil film pushed forward by the south wind in summer.