The work aims to study the degradation performance of polylactic acid (PLA) composite film and accelerate the degradation rate of PLA materials. Starch, sodium carboxymethyl cellulose (CMC) and polyethylene glycol (PEG) were mixed with PLA to prepare four different composite films. The light transmittance, mechanical properties and thermal properties of the films were measured. The group composition of the composite films was characterized by infrared spectrometer and the degradation performance was tested through immersion in phosphate buffer. The addition of composite materials changed the light transmittance of polylactic acid film and enhanced the tensile strength and elongation at break of the film. The IR spectra showed that there was no significant difference between the absorption peaks of PLA film and PLA composite film, which proved that the modified material had no chemical reaction with PLA. The DSC curve of the composite film showed that the temperature of Tm did not change significantly after the modifier was added. In terms of degradation performance, the degradation rates of PLA/starch composite films at the 70th day were 24.11%, 24.8% and 35.6%, respectively, according to the mass ratio of PLA to composite materials prepared at 9∶1, 7∶3 and 5∶5. The degradation rates of PLA/CMC composite films were 27.64%, 30.37% and 45.2%. The degradation rates of PLA/PEG composite films with PEG addition of 1%, 3% and 5% were 25.45%, 38.83% and 45.83%. The degradation rates of PLA/starch/PEG composite films reached 40.52%, 49.54% and 55.67%. The degradation performance of the composite films was much better than that of PLA films, with a degradation rate of 2.5%. The addition of modified materials can significantly enhance the degradation rate of poly (lactic acid) without affecting the structure of poly (lactic acid).