With superfine fruiting body powder of Ganoderma lucidum as raw materials, extraction temperature, extraction time, and solid-liquid ratios on the extraction of polysaccharides and the scavenging activity on DPPH radicals were investigated. The orthogonal experiments were used to optimize extraction process of Ganoderma lucidum polysaccharide by hot compressed water. The results showed that the optimal extraction conditions were as follows:extraction temperature 125℃, extraction time 30min,and the solid to liquid ratio 1∶50 (g/mL). Under these optimal conditions the yield of polysaccharides was 4.54%. The antioxidant activities results showed that the polysaccharides from Ganoderma lucidum possessed the scavenging abilities on DPPH radicals, which increased with the increased polysaccharides concentrations.