Objective:To genetically engineer an anti-H7N9 hemagglutinin Fab gene obtained by screening a full human Fab phage antibody library and to express it by antibody engineering, as well as verify its neutralizing activity to H7N9 avain influenza viruses. Methods: We screened a full human Fab phage antibody library using H7N9 avain influenza virus hemagglutinin and constructed IgG heavy and light chain expression vectors. Both vectors were transfected into 293 FreeStyle (293F) cells and the IgG antibody was expressed and purified. Then, the immunological activity was detected by ELISA assay and Western blotting assay, and the neutralizing activity was detected by microneutralization assay and prophylactic protection test in embryonated eggs. The hemagglutinin binding subunit was speculated by hemagglutination inhibition test. Results: A full human anti-H7N9 hemagglutinin Fab gene was successfully obtained and the IgG eukaryotic expression vectors were constructed. The sequences of both the heavy and the light chains of the antibody were correct and the antibody could bind to H7N9 hemagglutinin specifically. The antibody showed obvious neutralizing activity against H7N9 avain influenza viruses in microneutralization assay, and the neutralizing titer was 15.6 μg/mL. A dose of 200 μg IgG conferred a 100% survival rate in embryonated eggs. Hemagglutination inhibition test indicated that the IgG may bind the HA2 subunit of hemagglutinin. Conclusion: The reconstructed full human anti-H7N9 hemagglutinin IgG antibody could specifically recognize H7N9 avain influenza hemagglutinin and could obviously neutralize the virus, and laid a solid foundation for the further development of antibody drugs for the prophylaxis and treatment of avain influenza.