【Abstract】Objective:To study the relationship between the expression of CD28/CTLA-4 in peripheral and the mechanisms of preeclampsia. Methods ：Selected 35 PE patients with preeclampsia were preeclampsia group, 30 normal pregnant women as controls were investigated, we compared the expression of CD28/CTLA-4 in peripheral by flow cytometry Results: There was no statistical difference in the expression of CD28 between the two groups (P＞0.05 ) ; There was statistical difference of the levels of CTLA-4 between the two groups (P＜0.05 ), and Patients with preeclampsia in CD28 / CTLA-4 ratio lower than normal control group, significant difference was statistically significant (P <0.05) .Conclusion :The abnormal expression of CD28 / CTLA-4 in patients with preeclampsia can lead to abnormal category in T cell subsets, the dysfunction of maternal-fetal immune regulation, the immune tolerance imbalance, and the occurrence of preeclampsia.