Abstract: Based on studying the technological procedure of polyurethane (PU)-nanometer calcium carbonate (nano-CaCO ₃)/polyvinyl chloride (PVC) blending，and combining with PU reaction characteristics，nano-CaCO₃ with its surface treated by stearic acid was dispersed in liquefied 4，4'-diphenylmethane diisocyanate (L-MDI) by ultrasonic wave irradiation technology and stirring operation，and then the PU-nano-CaCO₃/PVC composite material was prepared by the one-step reactive ext rusion technology. The mechanical properties of PU-nano-CaCO₃/PVC were experimentally studied. The optimum toughening effectiveness is acquired when the mass ratio of PU to nano-CaCO₃ is 4∶1. There exists a synergism in toughening between nano-CaCO₃ and PU，and nano-CaCO₃ plays a function of reinforcement. When the mass ratio of PU to nano-CaCO₃ to PVC is 20∶5∶75，the composite has excellent comprehensive properties with the impact strength of 58.3 kJ/m² and tensile strength of 51.5 MPa.