Abstract: To explore the effects of Pseudomonas fluorescens ZX on controlling gray mold caused by B. cinerea in postharvest grapes and the possible modes of action. The control effect and growth curve of P. fluorescens ZX were determined in grapes (Vitis vinifera L.×V. labrusca L. ‘Kyoho’). Preventing and curing for B. cinerea was explored by the germ tube test, volatile antifungal test, and observation of scanning electron microscope in vitro condition. Using P. fluorescens ZX treatment, the incidence rate of grape was only 24.8%, which was significantly lower than that of the control group(incidence rate 64.67%), and the diameter of the lesion was the smallest. P. fluorescens ZX significantly inhibited spore germination and germ tube elongation of B. cinerea. The volatile substances produced by P. fluorescens ZX had strong antifungal activity. In addition, P. fluorescens ZX showed the activity of hyperparasitism on B. cinerea and could destroy the normal morphology of its hyphae. On the other hand, P. fluorescens ZX could rapidly colonize and grow on grape fruits, whether soaking or inoculation. All these finding suggested that P. fluorescens ZX could control postharvest gray mold on grapes via inhibiting the growth of B. cinerea. It provides a feasible option for preservation and decay control in postharvest fruit and vegetables.