This experiment was designed to investigate the effects of Yupingfeng polysaccharide on morphology of intestinal mucosa and expression of main immune and absorption genes of grass carp (Ctenopharyngodon idellus). A total of 750 healthy grass carp with an average body weight of (74.50±2.50) g were randomly assigned to 5 groups with 3 replicates per group and 50 fish per replicate. The first group (group Ⅰ) was the control group and fed a basal diet, and the remaining four groups (groups Ⅱ, Ⅲ, Ⅳ and Ⅴ) were experimental groups and fed experimental diets supplementing 0.8, 1.2, 1.6 and 2.0 g/kg Yupingfeng polysaccharide based on the basal diet, respectively. The pre-trial period was 7 days, and the formal trial period was 28 days. The results showed as follows:1) feeding for 14 days, the crypt depth of group Ⅴ was significantly lower than that of control group (P<0.05), and the villus height/crypt depth of group Ⅴ was significantly higher than that of control group (P<0.05). 2) On the trial day 7, compared with the control group, the relative expression level of interleukin-2 (IL-2) mRNA in head-kidney of groups Ⅲ and Ⅳ was significantly or extremely significantly increased (P<0.05 or P<0.01), the relative expression level of interferon γ (IFN-γ) mRNA in head-kidney of groups Ⅱ, Ⅲ, Ⅳ and Ⅴ was extremely significantly increased (P<0.01), and the relative expression levels of sodium glucose transporter 1 (SGLT-1) and glucose transport protein 2 (GLUT-2) mRNA in intestine of groups Ⅲ, Ⅳ and Ⅴ were significantly or extremely significantly increased (P<0.05 or P<0.01). 3) On the trial day 14, compared with the control group, the relative expression level of IL-2 mRNA in head-kidney of groups Ⅳ and Ⅴ was extremely significantly increased (P<0.01), the relative expression level of IFN-γ mRNA in head-kidney of groups Ⅱ, Ⅲ, Ⅳ and Ⅴ was significantly or extremely significantly increased (P<0.05 or P<0.01), and the relative expression levels of SGLT-1 and GLUT-2 mRNA in intestine of groups Ⅲ, Ⅳ and Ⅴ were extremely significantly increased (P<0.01). 4) On the trial day 21, compared with the control group, the relative expression level of IL-2 mRNA in head-kidney of group Ⅳ was significantly increased (P<0.05), the relative expression level of IFN-γ mRNA in head-kidney of groups Ⅱ, Ⅲ, Ⅳ and Ⅴ was extremely significantly increased (P<0.01), and the relative expression levels of SGLT-1 and GLUT-2 mRNA in intestine of groups Ⅱ, Ⅲ, Ⅳ and Ⅴ were significantly or extremely significantly increased (P<0.05 or P<0.01). 5) On the trial day 28, compared with the control group, the relative expression level of IL-2 mRNA in head-kidney of groups Ⅳ and Ⅴ was extremely significantly increased (P<0.01), the relative expression level of IFN-γ mRNA in head-kidney of groups Ⅲ, Ⅳ and Ⅴ was significantly or extremely significantly increased (P<0.05 or P<0.01), and the relative expression levels of SGLT-1 and GLUT-2 mRNA in intestine of groups Ⅱ, Ⅲ, Ⅳ and Ⅴ were significantly or extremely significantly increased (P<0.05 or P<0.01). On the whole, supplementing a certain amount of Yupingfeng polysaccharide in the diet can improve the morphology of intestinal mucosa, promote the expression of SGLT-1 and GLUT-2 genes in intestine, regulate the expression of IL-2 and IFN-γ genes in head-kidney, and then improve the intestinal absorption function and immunity of grass carp. In consideration of saving cost, the optimum supplemental level of Yupingfeng polysaccharide in the diet of grass carp is 1.6 g/kg.