Inclusion Criteria of Phase 1/2/3: 1. Males ≥ 18 years of age; 2. Have hemophilia B with ≤2 IU/dL (≤2 %) endogenous FIX activity levels; 3. Have had ≥100 prior exposure days (EDs) to any recombinant and/or plasma-derived FIX protein products based on historical data from the subjects' records/histories; 4. Have had bleeding events and/or injected with FIX protein products (including recombination and plasma source) during the last 12 weeks documented in the subjects' medical records; 5. Have no prior history of hypersensitivity or anaphylaxis associated with any FIX or IV immunoglobulin administration; 6. Agree to use a reliable barrier contraception method from the beginning of signing the informed consent to 52 weeks after administration. Exclusion Criteria of Phase 1/2/3: 1. Being positive for hepatitis B surface antigen (HBsAg) or hepatitis B virus-DNA (HBV-DNA). Being positive for hepatitis C virus antibody (HCV-Ab) or hepatitis C virus RNA (HCV-RNA). Subjects with medical history of hepatitis B or C can be regarded as negative only when 2 required samplings are conducted at least 3 months apart and both test results of indicators aforementioned are negative, i.e. subjects with natural clearance and anti-viral therapy clearance for hepatitis B or C are eligible; 2. Have potential liver diseases, such as previous diagnosis of portal hypertension, splenomegaly, hepatic encephalopathy or liver fibrosis (fibrosis stage ≥ 3); nodules or cysts were found by B ultrasound, or elevated alpha-fetoprotein was detected by laboratory tests. Subjects who are not eligible for the study if the abnormalities are clinically significant regarding to the medical judgement of the investigator; 3. HIV positive patients; 4. Have participated in a previous gene therapy research trial before screening, or in a clinical study with an investigational drug within 5 half-life of the investigational product, whichever is longer; 5. Have alcohol or drug dependence, or cannot stop drinking throughout the study; 6. Any concurrent clinically significant major disease or condition that the investigator deems unsuitable for participation in the study.