Abstract: The HA1 gene of H3N2 subtype swine influenza virus (SIV) was cloned into expression plasmid pET-30a. And the recombinant plasmid DNA was named as pET-HA1. Then it was transformed into E.coli BL21(DE3)， the recombinant protein was expressed in E.coli BL21(DE3)by induction of IPTG. The expressed HA protein was identified by SDSPAGE and Western blotting analysis. The results showed that HA1 protein was a 45 ku protein with immunogenicity. The purified HA protein was used to establish the indirect ELISA for detection of the antibodies against H3 subtype of SIV. The assay has excellent specificity， high sensitivity and excellent reproducibility. The total of 40 serum samples were randomly collected from field and evaluated by ELISA with recombinant HA1 and HI test， the coincidental rate between the two tests is 86.5%. These results showed that recombinant HA1 based ELISA is specific， sensitive and easy to perform for serologically diagnosis of SIV infection.