Abstract: Objective To construct Ag85A-HA2 prokaryotic expression vector, express the fusion protein and study the immunity efficacy of fusion protein against influenza A virus. Methods Ag85A-HA2 prokaryotic expression vector was constructed and induced with IPTG．The fusion protein was identified by SDS-PAGE and purified with His-Tag affinity chromatography. The BALB/c mice were immunized with fusion protein. Then the pathological section, lung index, lung inhibitory rate and death-protection rate were tested to evaluate the immunity efficacy of fusion protein. Results pET-32a(+)/Ag85A-HA2 prokaryotic expression vector was constructed successfully. And SDS-PAGE indicated that fusion protein was expressed correctly with a molecular mass of 70×103. The lung index and death-protection rate in experimental group were 39.30% and 80%, higher than that of control group. The pathological section also demonstrated that Ag85A-HA2 fusion protein had a protective effect on murine lungs. Conclusion Ag85A-HA2 prokaryotic expression vector was successfully constructed, inducible expression and the fusion protein had an immunity efficacy against influenza A virus in animal experiment.