Abstract : Objective To investigate the therapeutic effects of plasma diafiltration ( PDF) on coagulation dysfunction in severe patients. Methods A total of 596 severe patients who received blood purification treatment from I anuary 2018 to December 2021 were enrolled into this retrospective analysis. Among them, 22 severe patients with coagulation dysfunction who received 39 sets of PDF treatment were screened out. Their climical data before and after the treatment, such as biochemical indicators, routine coagulation test ，thromboelastography (TEG) and new molecular markers of coagulation, were collected and statistically analyzed. Results After PDF treatment, the prothrombin time (PT) and activated partial prothombin time ( APTT) of the patients with severe coagulation dysfunction were shorter than those before treatment, and their platelet count decreased with statistical signifcance (P<0.05 ), but no signifcant effect on thrombin time , fibrinogen levels, D-dimer levels and antithrombin activity was found ( P>0.05). After PDF treatment ,the R time and K time of TEG were shorter than those before treatment, but the MA value and coagulation index ( CI) were both higher than those before treatment with statistical significance ( P<0.05). The levels of plasma thrombomodulin, thrombin-antithrombin complex(TAT) and a2-pl asmin inhibitor-plasmin complex ( PIC) decreased significantly after PDF treatment compared with those before treatment ( P<0.05), but tssue plasminogen activator-inhibitor complex (t-P AIC) did not change sigificantly ( P>0.05 ). Conclusion PDF therapy may improve the functions of vascular endothelial cells and coagulation factors in the severe patients with coagulation dysfunction.