Abstract: Developing light-weight and high-efficiency absorbing composite materials is one of the important ways to solve the electromagnetic pollution. In this paper, ZnO-graphene (GR)/polylactic acid (PLA)/thermoplastic polyurethane (TPU) composite materials were prepared by a two-step method and the phase structure, micromorphology and electromagnetic characteristics of the composite were characterized by XRD, Raman spectroscopy, SEM and vector network analyzer. The effects of different combinations of ZnO/GR on the microwave absorbing properties of the composites were studied, and the synergistic mechanism was revealed. The results show that with the increase of the content of ZnO, the microwave absorbing effect increases at first and then decreases. Proper amount of ZnO dispersed in the matrix increases the defects of the composites enriching the heterogeneous interface, enhancing the interface polarization and dipolarization, and improving the microwave absorbing properties of the composites. When the content of ZnO is 2wt% , at 5.6 mm thickness, the minimum reflection loss is −49.2 dB and the effective absorption bandwidth is 2.0 GHz meaning the best absorption efficiency. The excellent absorbing effect is attributed to the good impedance matching and the synergy among the interface polarization loss, the dipolarization loss and the conductivity loss. In addition, the preparation process of ZnO-GR/PLA/TPU composite is simple and environment-friendly, and the component of absorbing agent can be adjusted which is expected to be used in the manufacturing of complex absorption structures.