In order to detect antibody against swine influenza virus (H1N1), HA1 region of hemagglutinin gene in epidemic swine influenza virus (H1N1) strain was amplified and subcloned into prokaryotic expression vector pET30a. Then recombinant HA1 protein was expressed by Escherichia coli BL21. The purified recombinant HA1 protein was obtained after the treatment of denaturing, refolding and affinity chromatography with immobilized nickel chelating NTA (Ni-NTA). An indirect enzyme-linked immunosorbent assay (ELISA) method was established using the purified protein as antigen. Then 785 swine serum samples collected during 2008-2009 were detected by this method, and the positive ratio was 15.54%. There were diversities among provinces (8%-47%). The diagnostic specificity and diagnostic sensitivity of this method arrived at 91% and 95% respectively, using the results of IDEXX ELISA kit as reference.