The invention relates to the technical field of in vitro diagnosis and detection, in particular to an application of a thionicotinamide adenine dinucleotide I to a homogeneous enzyme immunodiagnosticreagent. The diagnostic reagent is a glycocholic acid detection reagent and a CMPF reagent. The defect of relatively poor accuracy and repeatability of a detection result caused by relatively poor stability of the glycocholic acid reagent and the CMPF reagent in the prior art is overcome; a nicotinamide adenine dinucleotide II in the homogeneous enzyme immunodiagnostic reagent for homogeneous enzyme immunoassay is replaced with the thionicotinamide adenine dinucleotide I, so that the problem of relatively poor stability of the homogeneous enzyme immunodiagnostic reagent is effectively solved,the repeatability of the detection result of the reagent is improved, and the accuracy of the detection result is improved; and meanwhile, the anti-hemoglobin interference resistance of the reagent isimproved, the influence of a hemolysis phenomenon of a clinical sample on the detection result is weakened, and the detectability of the homogeneous enzyme immunodiagnostic reagent is improved, so that the test reagent is suitable for a conventional microplate reader, the detection cost is effectively reduced, and meanwhile, the usage amount of the reagent and raw materials is reduced.