Participants will be assigned to A or B groups with a scale of 1:1 based on a prospectively randomized treatment-sequence assignment, i.e. infuse SCT800 followed by Xyntha (group A), or the alternate sequence (group B). All participants who completed the SCT800HA1 study will enter the efficacy and safety study (Protocol No.: SCT800HA3).

Inclusion Criteria:

• 12 to 65 years old;
• The activity of the coagulation factor VIII (FVIII:C) ≤2%, and was previously treated with FVIII concentrate(s) for a minimum of 50 exposure days (EDs) prior to study entry
• Non-bleeding state (No clinical manifestations of active hemorrhage);
• Negative assays for FVIII inhibitors (<0.6 BU/mL);
• The platelet count is normal；
• Normal prothrombin time or INR ≤1.5；
• Given informed consent

Exclusion Criteria:

• Hypersensitivity to recombinant coagulation factor VIII concentrate or any of the excipients ;allergic to heterologous proteins (e.g. murine, bovine or hamster origin);
• Family history or history of FVIII inhibitors (≥0.6 Bethesda Units [BU] mL-1);
• Received an infusion of any FVIII for on-demand therapy or prophylaxis within 4 days prior to study entry (including rFVIII, plasma-derived factor VIII [pdFVIII], cryoprecipitate and whole blood);
• Significant hepatic or renal impairment (ALT and AST ≥2×ULN; BUN and Cr≥2×ULN);
• HIV seropositive;
• Abnormal hemostasis from causes other than hemophilia A；
• Patients with severe heart disease, including myocardial infarction, heart failure (III or higher level);
• Patients who received any anticoagulant or antiplatelet therapy within one week (including NSAIDs) or need to receive an anticoagulant or antiplatelet therapy during the period of clinical trials;
• Alcoholism, drug abuse, mental disorders and mental retardation;
• Elective surgery planned during the process of study;
• Patients who previously participated in the other clinical trials prior to study entry;
• The patient or parent/legal guardian is unable or unwilling to sign an informed consent form or to comply with the requirements of clinical protocol;
• Other conditions confirmed by the researchers, resulting in that patients are unable to benefit from clinical observation;