The invention belongs to the technical field of film separation and relates to a chitosan/nonionic surfactant cross-linked gel film with a sandwich structure and a preparation method thereof. The film is characterized in that the film has the sandwich structure, the upper and lower surface layers are arranged as cross-linked surfaces and a gel layer is arranged in the middle. The preparation method comprises the following steps: (1) uniformly mixing chitosan, nonionic surfactant and solvent under a certain temperature, paving on a polytetrafluoroethylene plate, and drying to remove the solvent to obtain a gel film; (2) soaking the gel film in the solution containing the cross-linking agent and catalyst for 0.1-6 hours and performing the surface cross-linking reaction on the gel film; (3) drying the cross-linked gel film in air for 24 hours, and then transferring into a vacuum drying oven, and processing for 24 hours at 30 DEG C, thereby acquiring the chitosan/nonionic surfactant cross-linked gel film with the sandwich structure. According to the preparation method provided by the invention, the upper and lower surfaces of the film are cross-linked, so that the chitosan/nonionic surfactant cross-linked gel film with the sandwich structure is formed, the nonionic surfactant is difficult to run off, the lasting stability of the physical structure and property of the film is ensured and the preparation method is fit for the separating of the carbon dioxide in the mixed gas and the recycling of the organic steam.