Abstract: Great successes have been achieved up on the postharvest biological control in recent 20 years. Hundreds of antagonists, which can effectively control postharvest diseases of fruits, have been found, and many of them have been successfully applied for commercial use. The mode of action of the antagonists has been unremittingly studied throughout the whole advance of postharvest biocontrol. The main four modes of action of the antagonists will be reviewed and the studying methods will be discussed in this paper.