In order to explore the effects of NaHCO₃ stress on antioxidant enzymes and tissue structure of gill and hepatopancreas of grass carp, three NaHCO₃ concentration groups (10, 20, 30 mmol/L) were used to stress grass carp with NaHCO₃, and the antioxidant enzymes (SOD, CAT) activity and histopathological observation of gill and hepatopancreas were carried out. The results showed that under NaHCO₃ stress, the activities of SOD and CAT in gill and CAT in hepatopancreas of grass carp increased first and then decreased within 72 h, and only the activity of SOD in hepatopancreas increased within 72 h. In each experimental group, the activities of antioxidant enzymes in the two tissues were significantly different from those in the blank group. Compared with the blank group, in the gill tissue of grass carp in the experimental group, the gill filaments were seriously folded and wrinkled, the PVC of the flat epithelial cells was seriously exfoliated, and the MRC of the mitochondria-enriched cells was swollen ； in the hepatopancreas, the swelling of the pancreatic cells, the increase of the intercellular space, the deviation of the hepatocyte nucleus and the decrease of the vacuolization were observed. Studies have shown that NaHCO₃ stress can affect the antioxidant level of grass carp and cause tissue damage to the gills and hepatopancreas of grass carp, and the degree of damage increases with the increase of concentration. This study could provide reference for the breeding and application of grass carp in saline-alkali waters.