The work aims to improve the stability of Zein modified by Gallic Acid (GA) at the interfaces of Pickering emulsion, endow it with antioxidant activity, and study the preservation effects of chitosan coating film on postharvest mangoes. The covalent compound (Zein-g-GA) of Zein and GA was prepared by alkaline treatment method. Zein-g-GA was used as an emulsifier to prepare Cinnamon Essential Oil (CEO) Pickering emulsion, and then the emulsion and chistosan solution were compounded and coated on the mango surface to study the effect of the composite film on the physiological and biochemical indicators of postharvest mangoes during room temperature storage and evaluate the preservation effect of the composite film. The particle size of CEO Pickering emulsion prepared with Zein-g-GA covalent as an emulsifier was uniform, about 3.618 μm. The chitosan/Zein-based Pickering emulsion coating film formed a film with good gas barrier on the surface of mango, reduced the water loss during storage, downgraded the weight loss rate of fruit, and prevented the drastic changes in hardness, pH and Total Soluble Solids (TSS). Meanwhile, the film inhibited the accumulation of MAD in mango, reduced the membrane lipid oxidation damage, and enhanced the antioxidant enzyme activity in the fruit, thereby maintaining the quality of mango during storage. The gallic acid modified Zein has the ability to stabilize essential oil, and chitosan/Zein-based Pickering emulsion film can be utilized as a coating packaging material to improve the preservation effects of postharvest mango and extend its shelf life. The chitosan coating film has broad development prospects in fruit preservation.