Based on observation data of atmosphere and Lake Taihu from 1985 to 2011 and the air temperature data (RCP4.5) of the model CNRM-CM5 output, partial leastsquares regression (PLSR) was used to analyze the annual relationships between chlorophyll-a (Chl-a) and air temperature, total nitrogen (TN), total phosphorus (TP), inorganic phosphorus (IP), dissolved silicon (Si), and to forecast the effect of future climate warming on Chl-a. The results showed that from 1980 to 2011, annual mean air temperature in Lake Taihu had been increasing at a rate of about 0.73 ℃·10 a^-1. Chl-a concentration also appeared an increasing trend at about 0.43 μg·L^-1 per year from 1985 to 2011. For nutrients, TN and Si had a more significantly increased trend than TP and IP. Relative to nutrients, air temperature was a dominant factor controlling the annual variation of Chl-a concentration according to the correlation analysis and PLSR. Furthermore, the variability of Chl-a concentration more depended on TN and Si than TP and IP. Under RCP4.5 Scenario, the future annual mean air temperature would increase at a rate of 0.19 ℃·10 a^-1 in Lake Taihu. Under current nutrient conditions, the phytoplankton biomass (Chl-a concentration) would also have a significantly increasing tendency. According to the 10-year running average value of Chl-a concentration, the increasing tendency would reach the peak value (34.18 μg·L^-1) during 2075-2085. If reducing the TN concentration to half of the present value, the peak value of Chl-a would be 28.91 μg·L^-1 during 2075-2085 and would be less than the minimum value of Chl-a concentration in the current conditions, which could mitigate the effect of climate warming on eutrophication.