Bleeding is the main clinical manifestation of the disease, and patients have a lifelong tendency to bleed spontaneously/slightly after injury/surgery for a long period of time; heavy cases can develop both after birth, and light cases develop a little later. 1, skin, mucous membrane bleeding Because the subcutaneous tissue, gums, tongue, oral mucosa and other parts are easy to be injured, so it is the site of bleeding. In young children, bleeding/hematoma after frontal collision is common, but bleeding from the skin and mucous membranes is not a characteristic of this disease. 2, joint hemorrhage Joint hemorrhage is a common clinical manifestation in patients with hemophilia A. It often occurs after trauma/walking too long/exercise causing synovial hemorrhage, mostly in the knee joint, followed by the ankle, hip, elbow, shoulder and wrist joints. Joint bleeding can be divided into three phases: (1) Acute phase: bleeding in the joint cavity and peri-articular tissues, resulting in localized heat, redness, swelling and pain in the joint. This is followed by muscle spasm, restricted movement, and the joint is mostly in a flexed position. (2) Total arthritis phase: In most cases, repeated bleeding prevents complete absorption of blood, and enzymes released from leukocytes and other components of the blood stimulate joint tissue, resulting in chronic inflammation and synovial thickening. (3) Late stage: arthrofibrosis/joint stiffness, deformity, muscle atrophy, bone destruction, and joint contracture leading to loss of function. Repeated bleeding in the knee joint often causes knee flexion, valgus, and fibular subluxation, forming a characteristic hemophilic pace. 3. Muscle hemorrhage and hematoma occur frequently in heavy hemophilia A, mostly after trauma/muscle activity for too long, mostly in muscles that are exerted. 4. Hematuria Patients with heavy hemophilia A may present with microscopic hematuria or carnal hematuria, mostly without pain and without history of trauma. However, if there is ureteral blood clot formation, there are symptoms of renal colic. 5.Pseudotumor (hemophilic hematocyst) The cyst can occur in any part, mostly in the thigh, pelvis, calf, foot, arm and hand, and sometimes in the eye. 6.Bleeding after trauma or surgery Various degrees of trauma and minor surgery can cause persistent and slow bleeding or hemorrhage. 7. Bleeding from other sites Gastrointestinal bleeding can be manifested as vomiting blood, black stool, bloody stool or abdominal pain, and most patients have primary lesions such as gastric and duodenal ulcers; hemoptysis is mostly related to primary lesions such as tuberculosis and bronchial expansion; epistaxis and sublingual hematoma are usually caused by injury in the oral cavity of patients with hemophilia A; sublingual hematoma can cause displacement of the tongue, and if the hematoma develops toward the neck, it often causes respiratory distress; intracranial hemorrhage is often the cause of death. 8, compression symptoms caused by hemorrhage and its complications Hematoma compression of nerves can lead to numbness, loss of sensation, severe pain and muscle atrophy in the area innervated by the compression; bleeding from the tongue, floor of the mouth, tonsils, posterior pharyngeal wall and anterior neck can cause upper respiratory obstruction, leading to respiratory distress and even death by asphyxia, and local vascular compression can cause tissue necrosis. Diagnostic criteria 1. Mostly male patients (female purets are rare), with or without family history, those with family history conform to x-linked recessive inheritance pattern; 2. Bleeding from joints, muscles, deep tissues, with or without history of abnormal bleeding after excessive activity, exertion, trauma or surgery, severe cases can be seen as joint deformity; 3. Positive laboratory test results.