A numerical model near the Changjiang River estuary was established based on FVCOM. A few numerical experimentations were conducted by different input condition, such as river discharge amount, wind, tide, baroclinic mode and background current. A series of analyses of direction change mechanism of the Changjiang River diluted water were taken by using the model result and observed data. It is shown by contrast different model results that the main external forces to make the diluted water turn to the northeast is the south wind. River discharge amount, tide and background current play quite an inconspicuous role in the direction changing process. River discharge amount and tide can only affect a small area near the estuary. Because of the stability of it, background current is not a main force for direction changing process. Baroclinic mode does not affect the path of diluted water too much.