The invention discloses a composite polymethacrylimide foam wave absorption material which is prepared by the following steps: (1) performing surface treatment on a wave absorber, namely uniformly mixing the wave absorber and a surfactant with a solvent, ultrasonically processing, drying to remove the solvent, and breaking and grinding to obtain a wave absorber subjected to surface treatment; (2) preparing expandable polymethacrylimide resin particles; (3) preparing the composite polymethacrylimide foam wave absorption material. The material is good in wave absorption performance, heat resistance and mechanical property, can be used for avoiding the defects of complex process, material waste and the like caused by a process that the material is machined to obtain a complex shape, can absorb electromagnetic waves to prevent electromagnetic wave interference, can be applied to the aspects of medical appliances, household appliances, electronic products, high-rise buildings, communication equipment, measurement equipment and the like, also can be used for stealth of various aircrafts, and has wide application prospect in the civil or military field.