In order to study the mechanism of enzyme-linked immunoassay for octapeptide cholecystokinin（CCK-8）,ELISA procedures were based on the pretreatment that polystyrene microplates were irradiated by ultraviolet and activated by glutaraldehyde prior to coating,and the binding nature of CCK-8 to microplates was revealed by different washing methods including dH₂O,PBS-T and SDS. The results showed that this pretreatment led to the covalent attachment of CCK-8 to the solid-phase steadily and fit to different sources of microplates. The treated microplates could be stored at least 4 weeks not to influence their ability of binding antigens.The intra- and inter- variation coefficients were 4.75% and 7.80% respectively.This polypeptide ELISA was characterized by covalent attachment between antigen and solid-phase carrier and was proved to be highly stable,reproducable and available.