The work aims to study the preservation effect of nanocomposite coating on sweet potato in order to improve the storage quality of sweet potato. Chitosan/Montmorillonite/whey protein isolate was used as raw materials to prepare edible nanocomposite preservative. The fresh-keeping effect of coating preservation on 'Xinxiang' type sweet potato was studied, and the coating composition was optimized orthogonally. At the temperature of (25±2)℃ and the relative humidity of (65±5)%, the nanocomposite coating preservative can slow down the increase of weight loss rate, soluble sugar content and total number of colonies of sweet potato, reduce the starch content loss, delay the Metabolism and maintain the quality of sweet potato well, thus achieving a more significant fresh-keeping effect. The best fit ratio of nanocomposite coating agent was obtained by orthogonal experiment:the mass concentration of chitosan was 20 g/L, the mass concentration of montmorillonite was 12 g/L, and the mass concentration of whey protein isolate was 60 g/L. A new sweet potato coating film is developed, which provides a new reference for the study of other nano-coated preservatives.