The invention discloses a film-mulching type preparation method of a self-thickening supporting agent. The film-mulching type preparation method comprises six steps of: preparing sucrose solution, washing the supporting agent with water or acid, placing the supporting agent into the sucrose solution to soak, drying till the water content is 3-5wt.% to obtain a wet supporting agent, preparing ethanol solution of a film-mulching material, uniformly mixing the wet supporting agent, the ethanol solution of the film-mulching material and a dispersing agent, fishing out the supporting agent treatedby the steps, drying, rolling and sieving. Compared with the existing mode for preparing fracturing fluid at a preparation station, the film-mulching type preparation method of the self-thickening supporting agent has the beneficial effects that the self-thickening supporting agent can realize online preparation of a construction well site, so that the operation cost of station and site equipmentand transporting vehicles is reduced; in addition, the type and the use amount of the film-mulching material can be selected and controlled according to the temperature of a fracturing oil reservoir and the degree of mineralization of filled water, so that the oil-reservoir adaptability of the fracturing construction technology of the self-thickening supporting agent is greatly improved.