To improve polysaccharide content of liquid fermentation mycelium of Ganoderma lucidum strain BS-1, the fermentation medium was optimized using response surface methodol. Firstly, a basic fermentation medium formula for response surface experiments was confirmed according to previous production On this basis, a Plackett-Burman design was applied to screen potential key factors from nine factors associated with mycelium polysaccharides content. Yeast extract and MgSO4 were identified as the main influence factors. Then, the steepest ascent test, central composite design, and response surface methodol. were applied to define more precisely the optimal composition of the fermentation medium, and a quadratic regression equation model was established using mycelium polysaccharides content as response values. Finally, the optimal medium formula with significantly improved polysaccharide content was obtained. The optimized medium was as follows: soybean meal 1, corn flour 1, glucose 1, yeast extract 0.845, Chinese yam 0.2, bran 0.2, KH2PO4 0.1, MgSO4·7H2O 0.132, and VB1 0.01%. The mycelium polysaccharide content of the optimized medium was 3.65%, 2.02-fold of that (1.81%) of previous basic medium.