The organic carbon production of phytoplankton near the Trestle monthly and at four stations quarterly in Lake Taihu fromJanuary 2007 to December 2007 was investigated, and its influence factors were analyzed. The results showed that there wereobvious temporal and spatial differences in the production of organic carbon in Lake Taihu. The high values of organic carbonproduction were recorded in spring and summer. The production of organic carbon was higher in the area where the phytoplanktonwas dominated by Cyanophyta and lower in the aquatic areas.