The closure project of the south branch of Lingkun in Oujiang River can bring out comprehensive benefits such as solving land demand, providing city development space, alleviating water resources shortage, shortening the length of sea embankment and improving the flood drainage condition in the east of Longwan area. Thus the closure project has been concerned by both government and people of Wenzhou since 1970s. On the basis of 2-D numerical simulation, this paper studies the influence on high water level, velocity, channel and harbor from Longwan to estuary mouth. The research result shows as follows: The south branch of Lingkun is in the state of siltation since 1960s. High water level during storm period would be increased by 0.03～0.05 m, velocity of Longwan harbor and channel decreased by 5%～10%, velocity of north branch and estuary mouth increased? by 8%～14% during spring tide and 10%～25% during flood time. The velocity of channel outside would be increased? by 0.08 m/s. It provides scientific basis for comprehensive development of Oujiang River estuary.