Using Spirulina powder as raw material， the optimal extraction conditions of Spirulina polysaccharide were investigated. The inhibitory effect， type and mechanism of Spirulina polysaccharide inhibition on tyrosinase were studied by enzyme kinetics， and the antioxidant capacity of Spirulina polysaccharide was evaluated by DPPH free radical method. Studies have shown that the best extraction effect of Spirulina polysaccharide could be obtained under the conditions of extraction time 2 h， the ratio of material to liquid is 1∶40， the extraction temperature is 90 °C， and the pH 8 is controlled to obtain the best extraction effect of Spirulina polysaccharide. The results of enzyme kinetics show that Spirulina polysaccharide It has a significant inhibitory effect on tyrosinase， and its IC50 is 1.193 mg/mL. Its inhibitory effect is reversible mixed inhibition， and its inhibition constant KI is 0.544 mg/mL. Spirulina polysaccharide showed a good scavenging effect on DPPH free radicals with an IC50 of 0.463 g/L and a free radical scavenging capacity of 83.24% of L-ascorbic acid at the same concentration.