Abstract: Water extraction and alkali extraction were used to optimize the extraction process of polysaccharides Salvia plebeia R. Br.. Antioxidant and hypoglycemic abilities of the two crude polysaccharides were compared in vitro. The results showed that the best process of Salvia plebeia R. Br. polysaccharide by water extraction was as follows: The extraction times were 4 times, the extraction temperature was 100 ℃, the ratio of solid to liquid was 1:20 g/mL, and the yield of polysaccharide was 2.86%. The optimal extraction process of Salvia plebeia R. Br. polysaccharide by alkali extraction method was as follows: Alkali concentration was 0.3 mol/L, extraction temperature was 100 ℃, solid-liquid ratio was 1:15 g/mL, and the yield of polysaccharide was 7.15%. The maximum scavenging rates of the two crude polysaccharides on DPPH free radical were 81.23% and 45.02% respectively, the maximum scavenging rates on ABTS⁺ free radical were 88.70% and 88.07% respectively, and the scavenging rates on superoxide anion ( \textO_\text2^- ) free radical were maintained at about 20% and 25% respectively, the inhibition rate of α-amylase increased in a dose-dependent manner. The scavenging ability of water extracted crude polysaccharide on DPPH free radical and ABTS⁺ free radical was higher than that of alkali extracted crude polysaccharide. Both polysaccharides had certain \textO_\text2^- free radical scavenging activity and α-amylase inhibition. In addition, through the comparison of infrared scanning spectra, it was found that the pyranose and carbonyl groups in the alkali extracted crude polysaccharide were destroyed compared with those in the water extracted crude polysaccharide, which may be the reason for the difference of their biological activities.