Hemophilia B is a hemorrhagic disease caused by the deficiency of clotting factor IX (FIX). Gene therapy might be the ultimate strategy for the disease. However, two main problems that should be solved in gene therapy for hemophilia B are immunity and safety. Self-complementary adeno-associated virus serotype 8 (scAAV8), a non-human primate AAV featuring low immunogenicity and high transfection efficiency in liver cells, might be a potential vector for hemophilia B gene therapy. A strong liver-specific promoter-1 (LP1) was inserted and mutant human FIX Arg338Ala was introduced into plasmid scAAV8-LP1 to develop an optimized AAV8 vector that expresses human clotting factor FIX (hFIX). The efficiency of scAAV8-LP1-hFIX administered through normal systemic injection or hydrodynamic injection was compared. A high expression was achieved using hydrodynamic injection, and the peak hFIX expression levels in the 5×10¹¹ and 1×10¹¹ virus genome (vg) cohorts were 31.94% and 25.02% of normal level, respectively, at 60 days post-injection. From the perspective of long-term (200 days) expression, both injection methods presented promising results with the concentration value maintained above 4% of normal plasma. The results were further verified by enzyme-linked immunosorbent assay and activated partial thromboplastin time. Our study provides a potential gene therapy method for hemophilia B.