Based on Gnome model , the trajectory and diffusion of oil released from anchorage out of Yangtze River Estuary were simulated. Tidal current filed modeled by FVCOM and dominant wind were used to drive GNOME model. The 40t medium crude was chosen to simulate the oil slick drifting track and diffusion area at flood fast tide, transition from flood slack to ebb tide, ebb fast tide and transition from ebb slack to flood tide within 4 d and the final distribution was given. The results show: oil slick drifts spirally toward southwest in 4 d under no wind; oil slick drifts spirally toward south in 4 d under northwest wind; oil slick drifts spirally in Hangzhou Bay(some stuck to the shore of Shanghai) under southeast wind ,specially, oil slick drifts northward when oil spill happened at flood fast tide; the drift distance under northwest wind is farther than under southeast wind while the diffusion area under northwest wind is smaller than under southeast wind.