• Subjects and statutory guardian must be able to understand the purpose and risks of the study and provide signed and dated informed consent;

• Be male and 12≤ age \<18 years of age, body wight ≥ 50kg;

• Have hemophilia B with ≤2 IU/dL (≤2 %) endogenous FIX activity levels as documented by a certified clinical laboratory at the time of screening. If the screening result is \>2% due to insufficient washout from FIX protein product, then the severity of hemophilia B may be confirmed by documented historical evidence from a certified clinical laboratory demonstrating ≤2% FIX coagulant activity (FIX:C) ;

• Had had ≥75 prior exposure days (EDs) to any recombinant and/or plasma-derived FIX protein products based on historical data from the subject's record/history;

• With ≤ 1:4 neutralizing antibodies and ≤1:200 binding antibodies against BBM-H901 capsid;

• Subjects with bleeding episode and/ or FIX agents infusion events within 12 weeks prior to screening;

• Have no prior history of hypersensitivity or anaphylaxis associated with any FIX or IV immunoglobulin administration;

• Have no measurable FIX inhibitor as assessed by laboratory; or documented no prior history of FIX inhibitor (family history of inhibitors will not exclude the subject) and no clinical signs or symptoms of decreased response to FIX administration;

• Have acceptable laboratory values:

∙ Hemoglobin ≥11 g/dL ;

‣ Platelets ≥100,000 cells/μL;

‣ AST, ALT ≤1.5x upper limit of normal at the testing laboratory;

‣ Bilirubin ≤1.5x ULN ;

‣ glomerular filtration rate eGFR ≥ 60ml/min.

⁃ For those subjects with sexual maturity, subject and statutory guardian must know that subjects must agree to use reliable barrier contraception until 52 weeks;

⁃ with good compliance to the schedule of visit and fill in the subject diary.