Astragalus polysaccharide (APS) is a soluble polysaccharide extracted from the root of Astragalus membranaceus that exerts many biological effects such as antibacterial and antioxidant effects, enhancing immunity and improving growth performance. To evaluate the potential effects of APS in Qihe crucian carp (Carassius auratus) as an immunopotentiator, the growth performance, viscera somatic index, antioxidant capability, and disease resistance of Qihe crucian carp administrated with APS were investigated in the present study. The experimental fish were randomly divided into four groups (30 fish per group with 3 repeats) and a 42 d growth trial was conducted. For the test groups (APS-1, APS-2, APS-3), fish were fed with basal diet supplemented with 500, 1,000, and 1,500 mg/kg APS, respectively. Meanwhile, the fish in the control group (CT) were fed with basal diet. The results show that dietary APS can increase the body weight growth rate (WGR) significantly (P＜0.05). The WGR in APS-3 group was highest and significantly higher than in the APS-1 or APS-2 group (P＜0.05). The specific growth rate of Qihe crucian carp was higher in the three test groups than in the control, but there was no significant difference among the APS-1, APS-2, and APS-3 groups, and there was no significant difference between the test groups and the control in feed conversion ratio. Previous studies suggested that APS could increase the viscera somatic index and promote the development and maturity of immune organs, thereby enhancing the immunity of organisms. However, the present study observed no significant difference in the kidney index or spleen index, and the liver index was significantly greater only in the Qihe crucian carp with the APS additive of 1000 mg/kg (APS-2 group) than in the control. This result indicates that APS additive of 1000 mg/kg could promote the development of the liver in Qihe crucian carp. Moreover, the enzymic activities of superoxide dismutase, catalase, and glutathione peroxidase (GPx) in the liver of fish in three test groups were higher than in the control. The highest values of SOD and GPx activities were presented in the APS-2 group, and were 46.6 U/mL and 41.8 U/mL, respectively. However, the activity of CAT in APS-2 group was the lowest among the three test groups, although it was significantly higher than in the control (P＜0.05). Additionally, the content of malondialdehyde (MDA) in the liver of Qihe crucian carp was significantly lower in three test groups than that in the control (P＜0.05), and the MDA content in APS-2 group was the lowest at 8.2 nmol/L. Therefore, APS additive in diets can enhance the antioxidant capacity of Qihe crucian carp, remove excessive reactive oxygen species, thus reduce oxidative damage, and decrease the content of MDA, which is the end product of lipid peroxidation. After challenge with Aeromonas hydrophila, the survival rate of Qihe crucian carp fed with APS additive was higher than that of the control. The survival rate of the fish fed with APS additive of 1,000 mg/kg was highest among three test groups at 75% after 96 h post infection. In conclusion, APS additive could improve the disease resistance of Qihe crucian carp against bacterial infection by promoting growth and increasing the antioxidant capability. Based on the comprehensive analyses of the results of this study, the appropriate dose of APS additive was 1000 mg/kg in feed of Qihe crucian cap, which could effectively prevent and control the fish diseases caused by A. hydrophila in aquaculture.