Abstract: 【Objective】 The study is aimed to investigate the effect of TSPSS on blood indexes of British thoroughbred horses in different pregnant stages. 【Method】 The number of 19 pregnant 7 month British thoroughbred horses of 480-550 kg heavy were selected in four groups according pregnant stage. TSPSS were supplemented for 5 consecutive days at 210, 240, 270 and 300 th pregnant day. Before administration and after being administrated 12 hours, the blood samples were collected and then blood routine, blood biochemistry, progesterone, estrogen and other indicators were tested to analyze the difference of blood indicators on five stages horses. 【Result】 The results showed that WBC was significantly higher than before (P< 0.05) in the third stage, but within the normal range. MID and LYMPH phases in the fourth phase were significantly lower than those before medication and the other phases (P < 0.05); The proportion of LYM in the fourth stage was significantly lower than that before and in other stages (P< 0.01); GRAN and GRAN ratio showed a significant increase in the four stages (P< 0.05), compared to that before, especially, the fourth stage was significantly higher than the first stage (P< 0.01). ALB in the third and fourth stages were significantly lower than that before treatment (P< 0.05); TBIL in the second stage was significantly higher than that before treatment and other stages (P< 0.05). The fourth stage of Ca²⁺ was significantly higher than that of the second stage (P< 0.05). E₂ in the fourth stage was significantly lower than that before treatment (P<0.05). 【Conclusion】 The results showed that the supplement of Chinese herbal medicine TSPSS had no effect on liver and kidney function of British thoroughbred horses aged from 7 to 10 months of gestation, which could effectively enhance the immunity and metabolism level of the body in the later period of pregnancy, promote the absorption of nutrients and have an effect on protecting fetus.