A circular enzyme detection method for detecting CG (cholyglycine) is characterized in that after endogenous glycine in a sample is removed, a circular reaction which is a vircular glycine circular reaction is performed; the concentration of CG is calculated by detecting the absorbance rising degree of NADH at 340 nm wavelength, and the determination result is obtained. According to the method, the circular reaction is produced on the basis of glycine, a reduced coenzyme I (NADH) amplification detection signal is produced through accumulation, determination is performed at 340 nm wavelength, and NADH is in direct proportion to the concentration of reactive CG. The invention further discloses a detection reagent based on the CG detection method. The reagent can be widely applied to clinical detection of CG. The reaction signal is enhanced through CG circulation, the reaction sensitivity is enhanced, and the reagent cost is reduced.