Objective:To investigate the changes and clinical significance of blood coagulation function and von Willebrand factor antigen (vWF:Ag) in patients with HELLP syndrome (hemolysis, elevated liver function, low platelet count).Methods:The clotting data of patients with severe preeclampsia and HELLP syndrome (observation group) admitted to the department of critical care medicine of the Fifth Center Hospital in Tianjin from May 2015 to December 2019 were retrospectively analyzed, and normal late pregnancy women with the same period were enrolled as the control group. The coagulation indexes such as prothrombin time (PT), activated partial thrombin time (APTT), antithrombin (AT), fibrinogen (Fib), D-dimer and plasma vWF:Ag level were compared between the two groups, and among patients with HELLP syndrome with different disease degree.Results:① Sixty-five patients with HELLP syndrome and 65 normal pregnant women with third trimester were included. Both groups were women of childbearing age, and there were no significant difference in the baseline data. ② The levels of Fib, D-dimer in both groups increased, but they were significantly higher in the observation group than those in the control group [Fib (g/L): 4.94 (4.76, 5.85) vs. 3.58 (2.97, 4.14), D-dimer (mg/L): 3.34 (2.55, 4.32) vs. 1.72 (1.29, 2.08), both P < 0.05], the AT was obviously reduced [62.00 (49.00, 73.00)% vs. 97.50 (90.75, 107.00)%, P < 0.01], and both PT and APTT were in the normal reference range in the two groups. In addition, the plasma vWF:Ag level in the observation group was significantly higher than that in the control group [516.50 (467.20, 563.00)% vs. 246.45 (189.95, 274.10)%, P < 0.01]. ③ According to thrombocytopenia, among the 65 patients with HELLP syndrome, 26 cases were mild [platelet count (PLT) > 100×10 9/L], 22 cases were moderate [PLT (50-100)×10 9/L], and 17 cases were severe (PLT < 50×10 9/L). With the aggravation of the disease, the D-dimer, Fib, vWF:Ag levels in the mild, moderate, severe patients significantly increased, while the AT level significantly decreased, and there was statistically significant difference between the two groups [D-dimer (mg/L): 2.63 (2.60, 2.73), 3.15 (2.55, 3.73), 3.84 (3.52, 4.23); Fib (g/L): 4.23 (4.06, 4.47), 4.72 (4.34, 5.04), 5.43 (5.14, 5.76); vWF:Ag: 465.20 (437.20, 495.40)%, 500.10 (472.40, 534.50)%, 543.50 (521.30, 563.00)%; AT: 67.50 (61.60, 78.00)%, 63.70 (53.30, 70.40)%, 54.40 (44.00, 61.20)%; all P < 0.05]. Conclusion:Patients with HELLP syndrome may show hypercoagulability and excessive expression of peripheral blood vWF:Ag level, which can induce platelet aggregation, leading to thrombocytopenia and thrombotic microangiopathy, and the clinicians should pay attention to that.