Abstract: To investigate the impact of a high-carbohydrate diet on glucose tolerance in grass carp, a total of 48 common grass carp and 48 grass carp fed with high carbohydrate diet, with an average weight of 374 g, were selected for a glucose tolerance test. The experimental fish were divided into two groups: a control group and a high carbohydrate group. The injection dosage was determined as 1.5 grams per kilogram of body weight, dissolved in 1 mL of PBS buffer. Additionally, 48 grass carp with similar body weight were chosen as the negative control group (PBS group) and injected with 1 mL of PBS buffer. Following the injection, blood glucose and insulin levels were measured at 0, 1h, 3h, 6h, and 12h, and liver samples were collected at the corresponding times to detect the expression of glucose-metabolism related genes. The blood tests showed that the high carbohydrate group exhibited the lowest blood glucose levels at the 0 hour. At the 1st hour, both groups reached peak blood glucose levels, with the high carbohydrate group demonstrating significantly lower levels than the control group. At the 12th hour, blood glucose levels in both groups returned to the normal range. Although insulin levels showed a slight increase post-glucose injection, the difference was not significant. RT-qPCR results showed that the expression levels of glut2 (glucose transporter), g6pase (glucose-6-phosphatase G-6-pase), and gys2 (glycogen synthase 2) genes were higher in the carbohydrate group compared to the control group at the 0h mark. Between the 1st and 3rd hours, expression of the gk (glucokinase) and gys2 gene in the high carbohydrate group was significantly higher than that in the control group. In summary, grass carp fed a high carbohydrate diet exhibited enhanced blood glucose clearance ability and improved glucose tolerance. The primary mechanism underlying rapid blood sugar clearance in the high-carbohydrate group grass carp appears to be the enhancement of glycogen synthesis.