The invention discloses a biodegradable polypropylene carbonate composite material and a preparation method thereof. The composite material is prepared from 50 to 90 mass parts of polypropylene carbonate and 10 to 40 mass parts of polyethylene terephthalate-1,4-cyclohexane dimethanol ester serving as raw materials by the following steps of: drying the raw materials at the temperature of between 45 and 55 DEG C for 5 to 10 hours; mixing the raw materials in a high-speed mixer for 0.5 to 3 minutes; and melting, mixing, extruding and granulating the mixed raw materials at the temperature of 65 to 170 DEG C. A thin film product prepared from the biodegradable PPC type composite material of the invention by blow molding has high physical and chemical properties; the glass-transition temperature of the PPC/PETG composite thin film is up to 69.2 DEG C; the thermolysis temperature of 5 weight percent of the material is up to 289.7 DEG C; the longitudinal tensile strength of the composite thin film is up to 28.6MPa and the transverse tensile strength is up to 16.7MPa; the longitudinal breaking elongation is up to 561.9 percent and the transverse breaking elongation is up to 755.3 percent; and thus the application range of the completely biodegradable polyester, namely the PPC in the agriculture, foods and packaging industry is expanded.