In order to understand the interactions between environmental factors and the algal biomass in Lake Chaohu, those rela-tively important environmental factors to alga biomass were extracted.Based on monitored water quality data of Lake Chaohu in 2008, cluster analysis, discriminate analysis and the recognition of pollution feature were carried out to reveal the relationships be-tween water environment factors and algal biomass.Results suggest that the Lake Chaohu can be divided into severe polluted area, moderately polluted area, and mildly polluted area from west to east.The Chl.a and dissolved total nitrogen are the indicative fac-tors describing the significantly spatial difference in water environment.The sequence of pollution classification for all the monito-ring sites are as follows:Nanfei river inlake area >Shiwuli river inlake area >Tangxi river inlake area >West lake center area >Paihe river inlake area >Hangbu river inlake area >Zhongmiao area >Zhaohe river inlake area >Bakou area >East lake center area >Ship factory >Zhonghan town area.The screened important environmental factors to algal biomass vary with seasons.TP, TN, temperature, NO₃^--N and NH₄⁺-N are closely related to algal biomass all the year round.