The invention discloses a liquid plastic film, and belongs to the technical field of agriculture. The liquid plastic film consists of the following components in percentage by weight: 1%-10% of pullulan polysaccharide, 1%-10% of polyglutamic acid and the balance of water, wherein the pullulan polysaccharide is prepared by fermenting aureobasidium pullulans of which the preservation No. is CGMCC No.7055, and the polyglutamic acid is prepared by fermenting bacillus licheniformis. The invention further discloses a preparation method and a use method of the liquid plastic film. The liquid plastic film is biodegradable and does not pollute environment, and after the plastic film is sprayed onto the surface of soil, the temperature of the soil can be raised, the evaporation of water is restrained, water content of the soil is increased, the salt content of the soil is reduced, and the soil can also be improved, so that the physicochemical property of the soil is better, and the growth of plants is promoted; besides, the liquid plastic film has the advantages of simple preparation method, low cost, good convenience in use, saving of labors and material, low cost and easiness in obtaining of raw materials, simple production equipment and technology, zero pollution in a production process, and the like.