The invention relates to a fully biodegradable aliphatic polycarbonate mulch film and a preparation method thereof. The mulch film comprises the following raw materials by weight ratio: 30-50 parts of aliphatic polycarbonate butanediol ester, 10-50 parts of starch, 10-50 parts of polylactic acid, 1-5 parts of herbicide, 1.0-3.5 parts of antiblocking agent, 0.5-6 parts of lubricant, 4.0-15 parts of plasticizer, 1.5-4 parts of heat-resistance stabilizing agent, 0.05-1.5 parts of anti-oxidant, 0.5-2.0 parts of coupling agent, 0.05-1.5 parts of biodegradation promoter and 0.5-5.0 parts of photodegradation agent. The Fully biodegradable aliphatic polycarbonate mulch film can be prepared by mixing and stirring the raw materials and extruding to granulate by a twin-screw machine. The fully biodegradable aliphatic polycarbonate mulch film of the invention has the advantages of low cost, good temperature toleration, temperature tolerance and water resistance, and is capable of regulating the degradation rate and has the function of weeding.