The present invention relates to the anti-human hepatocarcinoma McAb HAb18 heavy chain and light chain variable region genes, the polypeptides encoded by the same, as well as to their use in the preparation of a medicament for diagnosing and treating tumors or inflammation diseases. Based on the heavy chain and light chain variable region genes, various novel small molecule genetic engineering antibodies, including single chain antibodies, chimeric antibodies, Fab antibodies and the like can be constructed and expressed for the diagnosis and treatment of hepatoma.