Immunoprecipitation is mainly used for qualitative detection of antigens or antibodies. Its principle refers to the phenomenon of visible precipitates formed by soluble antigen and corresponding antibody in the presence of electrolytes in an appropriate proportion. The precipitation experiments designed according to this phenomenon mainly include flocculent precipitation test, ring precipitation test and precipitation test in gel. The precipitation test in gel can be divided into immunodiffusion test and immunoelectrophoresis technique according to the experimental method used.