Objective: To investigate the effect of low molecular weight heparin on coagulation function in patients with lower extremity fracture and the monitoring effect of Sonoclot coagulation and platelet function analyzer, and to provide guidance for clinical treatment of patients. Methods: Seventy-eight elderly patients with lower limb fracture treated in the Fourth Medical Center of PLA General Hospital from December 2017 to October 2019 were retrospectively analyzed. According to the treatment method, they were divided into a control group and a study group, 39 cases in each group. The control group was treated with conventional therapy, while the study group was treated with low molecular weight heparin to improve the coagulation function. The blood loss, postoperative bleeding volume, blood transfusion volume, and operation time of the two groups were compared, and the coagulation function indexes of the two groups before and after operation were observed. The monitoring effect of Sonoclot coagulation and platelet function analyzer was observed. The patients were followed up for 1 month, and the incidence of lower extremity deep venous thrombosis (DVT) was compared between the two groups. Results: There was no significant difference between the two groups in the amount of operative bleeding, postoperative bleeding, operation time and blood transfusion (P>0.05). Before operation, there was no significant difference in plasma prothrombin time (PT), plasma fibrinogen (FIB) and activated partial thromboplastin time (APTT) between the two groups (P>0.05). After operation, PT (14.01±0.41) s and APTT (39.59±2.45) s in the study group were significantly higher than those in the control group [(12.97±0.56) s, (37.26±3.41) s, respectively], and the difference was statistically significant (P<0.05). The level of FIB (2.24±0.51) g/L of the study group was significantly lower than that of the control group (3.01±0.48) g/L, and the difference was statistically significant (P<0.05). The monitoring results using common coagulation show that there were no significant differences in activated clotting time (ACT), clot rate (CR) and platelet function (PF) of patients between the two groups (P>0.05). The monitoring results using Sonoclot coagulation and platelet function analyzer show that the ACT value of the study group (187.67±29.27) s was significantly higher than that of the control group (169.12±22.34) s, and the difference was statistically significant (P<0.05). The CR (15.67±5.24) sig/min and PF (1.58±0.94) of the study group were significantly lower than those of the control group [(19.12±5.47) sig/min, (2.67±1.06), respectively], and the difference were statistically significant (P<0.05). The incidence of DVT in the study group was lower than that of the control group, and the difference was statistically significant (P<0.05). Conclusion: Low molecular weight heparin has a significant anticoagulant effect on the treatment of lower limb fractures, which can improve the patient’s hypercoagulability and prevent postoperative thrombosis. Sonoclot coagulation and platelet function analyzer can be used to monitor the coagulation effect on patients and to facilitate early diagnosis and treatment, so it worth promoting.