Abstract: Objective To explore the effects of Zishen Yutai pills on serum Th1/Th2 cytokines, sex hormone axis and pregnancy outcomes in patients with threatened abortion in the second trimester(20-27⁺⁶ weeks of gestation), and to analyze its efficacy in fetal preservation. Methods A total of 136 patients with threatened abortion in the second trimester(20-27⁺⁶ weeks of gestation) admitted to the Department of Obstetrics and Gynecology, the First Rongjun Special Care Hospital of Hebei Province from March 2021 to January 2024 were enrolled. Using the random number table method, they were divided into the control group and the observation group, with 68 cases in each group. The control group was treated with ritodrine hydrochloride, while the observation group received Zishen Yutai pills combined with ritodrine hydrochloride. Both groups received continuous treatment for 2 weeks. The clinical efficacy, time to resolution of clinical symptoms, sex hormone levels, endometrial receptivity indexes, Th1/Th2 cytokines, fetal preservation success rate and fullterm delivery rate were compared between the two groups. Results The total effective rate was 92.65% in the observation group, which was significantly higher than 76.47% in the control group（P< 0.05）. The times to resolution of abdominal pain, lumbago and uterine contractions, as well as the time to cessation of vaginal bleeding, were all significantly shorter in the observation group than in the control group（P< 0.05）. After 2 weeks of treatment, serum levels of progesterone（P）, estradiol（E₂）, interleukin（IL）-4 and IL-10 in the observation group were significantly higher than those in the control group（P< 0.05）, while levels of prostaglandin E₂（PGE₂）, resistance index（RI）, systolic/diastolic ratio（S/D）, pulsatility index（PI）, interferon-γ（IFN-γ） and IL-2 were significantly lower（P< 0.05）. The fullterm delivery rate and fetal preservation success rate in the observation group were significantly higher than those in the control group（P< 0.05）. Conclusion Zishen Yutai pills combined with ritodrine hydrochloride can effectively improve the clinical efficacy for patients with threatened abortion in the second trimester(20-27⁺⁶ weeks of gestation), alleviate clinical symptoms, regulate sex hormone levels, improve uterine hemodynamics and the imbalance of serum Th1/Th2 cytokines, thus increasing the fetal preservation success rate and full-term delivery rate.