The work aims to prepare polylactic acid (PLA)/thermoplastic polyurethane (TPU) composites with PLA as substrate to study the properties of composites and the effect of TPU content on it. Composites with different concentrations (17%, 20%, 25%, 33%and 50%) were prepared by blending of PLA and TPU with a twin-screw extruder. Infrared analysis of the composites were conducted and the effects of TPU on thermostabilities, thermodynamic properties and rheological properties of the composites were studied. With the increase of TPU, the thermostability and ductility improved;in the rheological experiment, the composites showed shear thinning and the properties of the composite were the best when the TPU content was 33%. The results show that the performance of PLA is improved after the addition of TPU.Composites can obtain the advantages of both materials without losing environmentally friendly.