The fermentation conditions for producing exopolysaccharides by Lactobacillus plantarum YW11 isolated from Tibetan Kefir were optimized. The experiment factors and levels were firstly selected by the single-factor test. And then, the influences of significant factors were evaluated using a fractional factorial design. Using the yield of exopolysaccharides as the optimization index, a quadratic polynomial regression equation forecasting model was set up by designing a Box-Behnken design involving of three factors and three levels and the method of response surface analysis,thus the optimized extraction conditions were obtained. The optimized results by the single factor test showed that:fermentation time 18 h, carbon source of lactose (15g/L), nitrogen source of soy peptone (15g/L), fermentation temperature of 32℃, inoculation rate of 3% and pH of 6.0. The significant factors at the analysis range were:soy peptone, pH and inoculation rate ,and the fermentation conditions optimized by response surface analysis were as follows:soy peptone concentration of 13.50g/L, inoculation rate of 2.70%, and pH of 6.27.The exopoly saccharides yield under the optimal condition was 131.26mg/L, near the theoretical value (129.915mg/L).