Left lower extremity edema is considered to be caused by deep vein thrombosis in the left lower extremity and has a higher incidence if the limb is swollen unilaterally and the circumference of both lower extremities differs by more than 3 cm. The specific causes include damage to the endothelium of the lower extremity after trauma, which tends to cause local deposition of platelets. In addition, patients who are bedridden for long periods of time or who have undergone internal fixation of long bone fractures in the lower extremities are prone to thrombosis. In some patients, the thrombosis is secondary to malignant tumors, and the hypercoagulable state of the blood is also a susceptible factor due to changes in the body’s internal environment. After diagnosis, the affected limb should be elevated promptly, and anticoagulation therapy should be actively administered to prevent pulmonary embolism due to dislodgment of the embolus. If necessary, an inferior vena cava filter should be implanted to intercept the thrombus and treat the comorbidity.