The work aims to graft chitosan and compound it with thyme essential oil and then study the preservation effect of composite coating on litchi during storage. Activator reagents were utilized to graft chitosan with quaternary phosphate salt and sorbic acid to improve its water solubility and antibacterial activity, and then the composite coating solution was prepared with nano cellulose and thyme essential oil. The composite coating solution was used for the preservation of litchi at room temperature, and the pH, weight loss rate, vitamin C content, total phenol content, titratable acid, soluble solids and other indicators of litchi were tested and analyzed. By comparing the composite coating with the control group treated with ultrapure water, prochloraz, chitosan and other methods, the effect of composite coating on the storage quality of litchi was explored. Compared with the control treatment group, the modified chitosan/thyme essential oil composite coating had better barrier performance, which could effectively reduce the weight loss of litchi, reduce the loss of water and nutrients, and inhibit mold growth and browning. The modified chitosan/thyme essential oil composite coating has the ability to maintain the quality of litchi and extend the shelf life of storage, and the coating solution is economical in source, has high practical popularization and development prospects, and achieves economic, green, efficient and lasting preservation effect.