This article reports a case of acute myelomonocytic leukemia (AML-M₄, CBFB gene positive) with lower limb microthrombus formation after haploidentical hematopoietic stem cell transplantation, and summarizes the experience of diagnosis and treatment. The patient received achieved complete remission (CR) after routine chemotherapy, but relapsed 2 years later and underwent a haploidentical hematopoietic stem cell transplantation. During routine treatment after transplantation, the patient’s coagulation related indicators, including D-dimer (D-D), antithrombin Ⅲ (AT-Ⅲ), von Willebrand factor (vWF), fibrinogen degradation products (FDP) and fibrin monomer (FM), were dynamically observed. The patient experienced jaundice and elevated transaminases around 100 days after transplantation, and underwent plasma exchange treatment three times through the right lower limb femoral vein catheterization. After removing the venous catheter for one week, there was left ankle concavea pitting edema of the left ankle. Vascular ultrasound examination indicated the formation of microthrombus in the superficial venous plexus of the gastrocnemius muscle in the left lower limb. D-D, vWF, FDP, FM and other indicators were increased, while AT-Ⅲ levels was decreased. After 2 weeks of oral administration of 5 mg/d berritol for antithrombotic treatment, the above coagulation indicators gradually returned to normal, and the left lower limb intermuscular venous plexus thrombosis and limb swelling disappeared. Therefore, dynamic monitoring of coagulation indicators, such as D-D, AT-Ⅲ, vWF, FDP, and FM may serve as diagnostic indicators for predict transplant related microthrombus and hypercoagulable status, providing an experimental basis for effective anticoagulant treatment in clinical practice.