Abstract: In order to improve the extraction rate of crude polysaccharides from Astragalus offcuts, in the experiment, the extraction process of crude polysaccharide from Astragalus offcuts was optimized using one-way test and response surface method. One hundred healthy carp with close body weight were randomly divided into blank control group, Chinese medicine control group, low dose group, middle dose group and high dose group. The blank control group was fed with basal feed; the Chinese medicine control group was fed with basal feed containing 0.1% crude polysaccharide from Astragalus offcuts; the low-dose group was fed with basal feed containing 0.1% crude polysaccharide from Astragalus offcuts; the medium-dose group was fed with basal feed containing 0.2% crude polysaccharide from Astragalus offcuts; the high-dose group was fed with basal feed containing 0.4% crude polysaccharide from Astragalus offcuts; and the dietary supplementation period lasted 42 days. At the end of the experimental period, blood was taken from the tail vein of carp, and the activities of lysozyme（LZM）, alkaline phosphatase（AKP） and superoxide dismutase（SOD） were determined. The results showed that the maximum extraction rate of crude polysaccharides from Astragalus offcuts was 7.67% under the conditions of extraction temperature of 93 ℃, extraction time of 2.8 h, and material-liquid ratio of 1∶30（g/mL）. The LZM, AKP and SOD activities of the low-dose and medium-dose groups with 0.1% and 0.2% of crude polysaccharide from Astragalus offcuts were significantly higher than those of the blank control group（P＜0.05）; the medium-dose group had the greatest LZM and SOD activities. AKP activity was significantly higher（P＜0.05） in the low dose group than those in the blank and Chinese medicine control groups. The LZM activity in the high-dose group was significantly lower than that in the medium-dose group（P＜0.05）; the SOD activity was significantly lower than that in the low-dose and medium-dose groups（P＜0.05）; and the AKP activity was lower than that in the low-dose and medium-dose groups, but the difference was not significant（P＞0.05）. The results suggested that a higher content of crude polysaccharides could be extracted from Astragalus offcuts after optimizing the extraction process of crude polysaccharides from Astragalus offcuts by response surface methodology; and the addition of 0.1%-0.2% crude polysaccharides from Astragalus offcuts in the basal feeds could obviously improve the immune ability of carp.