Objective： To study and compare the composition， blood sugar lowering effect and composition of BPS， LPS and MPS. Methods： Bailingongfu was selected as representatives of black tea. The composition， molecular weight and monosaccharide composition of plant polysaccharides were determined. The mice diabetes model was induced by streptozotocin， and metformin was used as a positive control to study the hypoglycemic effect of plant polysaccharides， qPCR was used to determine the expression level of related genes in mice liver， and the serum transaminase level in mice was determined. Results： The molecular weights of BPS， LPS and MPS are 8 745， 22 410 u and 34 430 u， respectively. The selected plant polysaccharides have hypoglycemic effect， the fasting blood glucose decline rates of BPS， LPS and MPS were 61.6%， 52.8% and 53.8%， respectively. Plant polysaccharides can increase the activity of enzymes related to glycolysis and down-regulate the expression of Foxo1， G6Pc， PEPCK and TXNIP genes in mice. The hypoglycemic effect showed the regularity of black tea > mulberry leaf > Lycium barbarum fruit. Conclusion： Under the selected dose condition， the plant polysaccharides didn′t show hepatotoxicity. The research on the hypoglycemic effect of the selected black tea polysaccharide is better than the mulberry leaf polysaccharide and the Lycium barbarum fruit polysaccharide.