Abstract: In order to understand the optimal fermentation technology of complex probiotics on compound Chinese herbal medicine feed additives, and investigate the acute and subchronic toxicity of fermented compound Chinese herbal feed additives on mice, the yield of total flavonoids in fermented Chinese herbal medicine（determined by sodium nitrite-aluminum nitrite-sodium hydroxide method） was used as an indicator, and the proportion of mixed strains, inoculation amount of bacterial solution, fermentation temperature and fermentation time of mixed bacteria were optimized by single factor experiment and orthogonal test, and the mass concentration of total flavonoids in fermented Chinese herbal medicines was measured under the optimal process parameters. In the acute toxicity test, 40 mice were randomly divided into high dose（gavage 20 mg/kg according to body weight）, medium dose（gavage 15 mg/kg according to body weight）, low dose（gavage 10 mg/kg according to body weight） and control group（gavage 10 mL/kg sterile saline according to body weight）, which were continuously observed for 7 days after gavage. The mental state, diet, behavior and death of the mice were recorded every day. In the subchronic toxicity test, 40 mice were randomly divided into high dose（gavage 15 mg/kg according to body weight）, medium dose（gavage 10 mg/kg according to body weight）, low dose（gavage 5 mg/kg according to body weight） and control group（gavage 10 mL/kg sterile saline according to body weight）. Intragastric administration was performed once a day for 90 days. After the end of administration, the observation continued for 28 days. On the last day, blood and organs of mice were collected; organ coefficients were calculated; serum biochemical indexes were detected and histopathological changes were observed. The results showed that the optimum fermentation conditions were as follows: the ratio of Bacillus amyloliquefaciens to Lactobacillus casei was 1∶4（V/V）; the inoculum amount was 1.0%; the fermentation temperature was 37 ℃, and the fermentation time was 72 h. The average mass contentration of total flavonoids in Chinese herbal medicine after fermentation was 3.032 g/L, which was in line with expectation. In the acute toxicity test, no median lethal dose(LD₅₀) was detected. In the subchronic toxicity test, there was no significant difference in the organ coefficient and serum biochemical indexes（except for aspartate aminotransferase and alkaline phosphatase） of mice in each group at 28th day after drug withdrawal（P＞0.05）. The results indicated that fermented Chinese herbal feed additives was safe and harmless.