The water quality of Wuliangsuhai Lake was evaluated based on the measured data on July 29,0, and through calculating the fractal dimension of single index of water quality. The fractal dimension exponent can be determined by the maximum likelihood classification principle, and adopting weighted average value. The results showed that the fractal theory can be used in the water quality eraluation of lakes due to the evaluation result for Wuliangsuhai Lake is consistent with the measured data.