In order to study the mechanisms of different inhibitors such as 4-HR, oxalic acid, phytic acid, and benzoic acid on apple polyphenol oxidase (PPO), chlorogenic acid was chosen as substrates in a model apple juice. The results show that the inhibitory mode of 4-HR and oxalic acid were found to be of the competitive type since Km values increased with increasing 4-HR and oxalic acid concentration and Vmax value remained unchanged. Phytic acid was the mixed inhibitor whereas benzoic acid was a noncompetitive inhibitor. This study will provide a theoretical basis for controlling enzymatic browning in apple juice.