Abstract: More than 1400 sampling plots of 151 sites distributed throughout 13 counties "were surveyed, 88 families, 301 genera and 555 species ( including 15 varieties ) were recorded and sampled.The vicious and main weed species in the Various crop fields and habitates -were determined by the frequencies and dominances of weeds.The results showed that the main features of the weed flora of Taihu agricultural area were as follows; abundant and widely spreaded in species; highly diversified in family and genera; remarkable geographical characteristics of middle and lower Yangtze River valley; dominant anual lifeform; large proportion of hydrophyte and hygrophyte; obvious companionate with crops; sensitive to the environmental factors both ecofo-gical and cultivational.