The invention provides a polybutylene adipate terephthalate/polymethyl ethylene carbonate full-biodegradable composition and a preparation method thereof. The material comprises the following raw materials in parts by weight: 50-82 parts of polybutylene adipate terephthalate resin, 8-40 parts of modified PPC, 0.3-3 parts of a lubricant, 5-15 parts of a macromolecular plasticizer and 1-5 parts of an inorganic filler; wherein a modifier of the modified PPC is selected from one or more of maleic anhydride and butanedioic anhydride. According to the invention, the polybutylene adipate terephthalate resin is mixed with the modified PPC and other auxiliary agents; the flowability and the film-forming property of the casting film are improved; an obtained plasticizer has good compatibility with PBAT and PPC, can be completely biodegraded, is low in volatility, and is combined with the above specific ratio, so that the prepared film has high tensile and tearing strength, good elasticity modulus, good elongation at break, good barrier property, good biodegradability and uniform tensile properties in all directions.