The invention relates to a preparation method of a high-thermal-insulation/soil-moisture-preservation degradable agricultural mulching film material. The agricultural mulching film is prepared from PBAT (poly(butyleneadipate-co-terephthalate)), PPC (polypropylene carbonate), PLA (polylactic acid), an anti-degradation master batch, an opening agent, a compatilizer, a chain extender and a starch surface treating agent. The preparation method comprises the following steps: proportionally weighing all the raw materials, carrying out drying pretreatment on the PBAT, PPC, PLA and anti-degradation master batch, carrying out batch mixing, sending the mixture into a double screw extruder through different agravic weighers, melting by heating, carrying out extrusion, drawing, cooling, granulation and drying to obtain granules, and sealing and storing in an aluminum-plastic packaging bag. The film blowing experiment proves that the degradable plastic can completely satisfy the mulching film demands. The minimum thickness of the film can reach 6 mu m. The preparation method has the advantages of stable film blowing technique and controllable size of the blown film. The mulching film material has the characteristics of favorable mechanical properties, high thermal insulation property, high soil moisture preservation property, high light transmittance, lower price and the like, can be completely degraded into water and carbon dioxide after being buried underground after use, and thus, satisfies the environmental requirements.