Possible causes of left calf pain include thromboembolic vasculitis, deep vein thrombosis of the lower extremities, osteoarthritis of the knee, diabetes mellitus and so on. 1. Thromboembolic vasculitis: closely related to smoking, it often causes middle and small arterial and venous vasculopathy in the limbs, which can cause intermittent claudication, lower limb rest pain, ulceration and other symptoms. 2. Lower extremity deep vein thrombosis: due to braking, high blood coagulation caused by deep vein thrombosis of the lower extremities, the lower extremity muscle cells reduce blood supply, oxygen supply caused by lower extremity pain. 3. Osteoarthritis of the knee: a disease characterized by degeneration of the cartilage of the knee joint and osteophytes, which can cause pain and swelling of the knee joint of the left lower limb and hidden pain in the calf. 4. Diabetes mellitus: when long-term blood sugar control is not good, peripheral vascular disease can occur, causing pain in the lower limbs. It is recommended that when left calf pain occurs, consult a doctor in time to identify the cause and standardize the treatment under the guidance of the doctor.