Microwave-absorbing materials that are used for stealth weapons and equipment should have excellent characteristics of strong absorption, a wide absorption bandwidth, low thickness, and light weight. Ti 3 C 2 T x , as a twodimensional (2D) MXene material, shows great potential in the field of microwave absorption. However, MXene has problems of impedance mismatch, a narrow absorption bandwidth, and poor absorption performances. In this study, we designed a series of ZIF-8/MXene-based microwave-absorbing materials known as porous ZnO/MXene nanocomposites, which were synthesized by an in situ composite method before being annealed under vacuum. Then, the structure and performances of porous ZnO/MXene were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and using a vector network analyzer (VNA). We investigated the influences of the mass ratio, microstructure, morphology, and microwave absorption performances of the samples on raw materials. As a result, ZnO/MXene nanocomposites with a mass ratio of Zn 2+ / MXene = 2:1 showed the optimum microwave absorption performance. The minimum reflection loss was −34.31 dB at 8.8 GHz (thickness 1.0 mm), and the effective absorption bandwidth was 3.47 GHz from 13.49 to 16.96 GHz.