Potato starch-based composite films were prepared by casting using potato starch, pullulan, gelatin as film forming material, calcium chloride as cross-linking agent, and glycerol, sorbitol, and polyethylene glycol as plasticizer. The effects of three kinds of plasticizers on physical and mechanical properties of composite films were studied. The results showed that tensile strength and Young's modulus of the composite films decrease significantly with plasticizer contents; elongation increases significantly with glycerol and sorbitol contents; effect of polyethylene glycol on elongation is not obvious; water vapor permeability and water solubility of composite films increase with plasticizer contents; polyethylene glycol can reduce the light transmission rate of the composite films significantly.