The work aims to investigate the effect of chitosan (CS) concentration and cinnamon essential oil (CEO) addition on the properties of composite films (mechanical properties, oxygen permeability, moisture absorption, resistance to oxidation) and the optimal effect of composite films on the storage quality of walnuts. This study adopted CS with different mass concentrations (1%, 1.5%, 2%) and CEO with different mass concentrations (0.1%, 0.2%, 0.3%, 0.4%) to prepare composite films. Various properties of the films were characterized. Walnuts were treated with the optimal ratio of composite films to determine the changes in nutritional and oxidative related indicators during storage. The results showed that the composite film prepared with 1.5% concentration of CS and 0.3% concentration of CEO had good mechanical properties and resistance to oxidation. Compared with the control and pure CS treatment, the walnut treated with the film could effectively maintain its water content, soluble protein, fat content, and high peroxidase (POD) activity during storage; At the same time, it inhibited the increase in acid value, malondialdehyde content, and polyphenol oxidase (PPO) activity of walnuts during storage. Therefore, adding CEO can effectively improve the properties of chitosan films, and the CS-CEO composite film prepared in the optimal proportion can better maintain the nutritional and antioxidant quality of walnuts during storage.