This study is a multi-center, open-label, single-arm trial to evaluate the efficacy,safety and pharmacokinetics of SCT800 in regular prophylaxis and perioperative treatment in patients (≥12 years old) with severe hemophilia A who have been previously treated with coagulation factor VIII(FVIII:C) . This study includes two phases: the screening period and prophylaxis period.Prophylaxis with 25 - 50 IU/kg of SCT800 shall be administered once every other day or three times per week starting from V1 and prophylaxis with SCT800 shall continue for 24 consecutive weeks.

After subjects pass screening, prophylaxis with 25 - 50 IU/kg of SCT800 shall be administered once every other day or three times per week for 6 months. Subjects shall receive FVIII intravenous injection treatment at the study site or at home. During the study prophylaxis treatment period, subjects should return for visit every four weeks, namely for Visit (V) 2 (4 weeks ± 4 days), Visit 3 (8 weeks ± 4 days), Visit 4 (12 weeks ± 4 days), Visit 5 (16 weeks ± 7 days), Visit 6 (20 weeks ± 7 days), Visit 7 (24 weeks ± 7 days) and end-of-treatment (EOT) visit (+ 14 days). Of which, blood collection shall be carried out during the screening period and in V1, V2, V4, V7 and the EOT visit for FVIII inhibitor assay; blood collection shall be carried out before and after the completion of SCT800 infusion in V1, V4 and V7 for incremental in-vivo recovery (IVR) assay.

FVIII:C activity shall be monitored before injection and 15minutes(min), 30min, 1h, 3h, 6h, 9h, 12h, 24hours(h), 28h, 32h and 48h after injection at V1 and V7. Then pharmacokinetics parameters (incremental in-vivo recovery, t1/2 etc.) of SCT800 shall be calculated and evaluated.

5 subjects may receive elective surgical treatment within the prophylaxis treatment period (after the first drug administration in day 0).

Inclusion Criteria:

• Aged ≥12 years old and ≤65 years old;
• Male patients who are clinically diagnosed with severe (laboratory tested FVIII:C <1%) hemophilia A, including historical FVIII:C <1%;
• Previously received FVIII treatment (prophylactic or bleeding treatment), have the relevant records and are verified to have accumulated exposures days( EDs) ≥150 days;
• The bleeding treatment records of at least 3 months before screening can be obtained;
• Negative FVIII inhibitor assay results (laboratory tested Nijmegen-Bethesda assay result <0.6 BU(Bethesda unit)/mL);
• The prothrombin time is normal or international normalized ratio (INR) ≤1.5; 7. Platelet count ≥100 × 109/L;

Exclusion Criteria:

• Known allergy to recombinant coagulation factor VIII concentrate or any excipient; known allergy to bovine, rodent or hamster bovine;
• Has a history or family history of blood coagulation factor VIII inhibitor;
• Clinical liver function test (glutamic-pyruvic transaminase, glutamic-pyruvic transaminase) ≥ three times the upper limit of normal (ULN) or clinical kidney function test (blood urea nitrogen, creatinine) ≥ three times the ULN;
• Patients clinically diagnosed with active Hepatitis B or Hepatitis C;
• Patients with other coagulation dysfunction diseases in addition to hemophilia A;
• Patients with severe heart disease, including myocardial infarction and cardiac dysfunction of class III or above;
• Patients who previously experienced intracranial bleeding;

Hemophilia A is a kind of sex chromosome recessive genetic disease and ofter occurs in male.