This experiment was conducted to study the effects of dietary alfalfa flavonoids extraction supplemental level on growth performance, organ development and blood biochemical indexes of Yangzhou geese at the age of 28 to 70 days. Two hundred and forty 21-day-old healthy male geese with similar body weight were randomly distributed into 4 groups with 6 replicates per group and 10 geese per replicate. Geese in the control group were fed a basal diet and the others in the experimental groups (groups 1, 2, and 3) were fed experimental diets supplemented with 150, 300 and 450 mg/kg alfalfa flavonoids extraction (the concentration of it was 81%), respectively. The experiment had 7 days for pre-test and 42 days for formal test. The results showed that the final body weight and average daily intake of group 2 were significantly higher than those of other groups ( P < 0.05). The average daily gain of group 2 was significantly higher than that in the control group and group 1 ( P < 0.05). There was no significant difference in feed-to-gain ratio between each group ( P > 0.05). Pre-slaughter live weight, carcass weight, slaughter rate, semi-eviscerated weight, semi-eviscerated rate, eviscerated weight, eviscerated rate, leg muscle weight and leg muscle rate had no significant difference between each group ( P > 0.05). The breast muscle weight and ratio of each test group were significantly higher than those in the control group ( P < 0.05) and the group 2 was the best. The abdominal fat weight and ratio in the group 1 were significantly higher than those in the control group and group 3 ( P < 0.05) and the tibia weight in the group 2 was significantly higher than that in the control group and group 1 ( P < 0.05); There were no significant differences in heart weight, liver weight and the gland stomach weight among all groups ( P > 0.05). Spleen weight in test groups was significantly higher than that in the control group ( P < 0.05). The bursa weight and muscular stomach weight in the group 2 were significantly higher than those in the control group and group 1 ( P < 0.05). In serum, total cholesterol, triglycerides, low-density lipoprotein and urea nitrogen in the group 2 were significantly lower comparing with those in the control group ( P < 0.05). High-density lipoprotein in the group 2 was significantly higher than that in other groups ( P < 0.05). There were no significant differences in total serum protein, albumin, globulin and albumin/globulin among all groups ( P > 0.05). Alanine aminotransferase and aspartate transaminase (AST) in groups 2 and 3 were higher than those in the group 1 and control group but not obvious ( P > 0.05) and alkaline phosphatase (ALP) in groups 1 and 2 was higher than that in the control group and group 3 ( P > 0.05). It is concluded that alfalfa flavonoids extraction added in dietary feed improve the growth performance, organ development and blood biochemical indexes of Yangzhou geese. It is concluded that 300 mg/kg supplemental level of the dietary alfalfa flavonoids extraction is optimal in this experiment.