The paper aims to improve the performance of polylactic acid (PLA)/thermoplastic starch (TPS) blended composite film. The effects of acetyl tributyl citrate (ATBC) and epoxidized soybean oil (ESO) plasticizer on mechanical properties, moisture permeability, light transmittance, microscopic structures and thermodynamic properties of the composite. The addition of plasticizer could significantly change the mechanical properties of the composite film. When the dosage of ATBC increased from 10% to 20%, the elongation at break of the film increased by 38 times, while the tensile strength was only 36%. The addition of single ATBC or ESO had a substantially uniform effect on the moisture permeability and light transmission of the composite film, and the effect was superior to the blended plasticizer. The two plasticizers had certain synergistic effects, but using simultaneously could cause a decrease in the onset temperature of thermal decomposition. For the single plasticizer, ATBC was better than ESO. However, due to their poor compatibility, ATBC/ESO mixture did not exhibit obvious advantages over the single plasticizer ATBC under the same dosage. The composite film with an ATBC addition of 20% has the best overall performance.