The invention discloses a ZnO/Fe/Fe3C/C (zinc oxide/iron/iron carbide/carbon) composite electromagnetic wave absorbent, and also discloses a preparation method of the ZnO/Fe/Fe3C/C composite electromagnetic wave absorbent. The preparation method comprises the following steps of preparing FeIII-MOF-5 by a reflux method: adding reaction materials of ferric acetylacetonate, zinc nitrate, terephthalic acid and PVP (polyvinyl pyrrolidone) into a mixed solvent of N,N-dimethylformamide and ethyl alcohol, completely dissolving, and refluxing at certain temperature; centrifuging, washing and drying a product after reaction, so as to obtain a precursor FeIII-MOF-5; calcining the precursor product under the inertia environment at the temperature of 550 to 750 DEG C, so as to obtain a final product. The porous composite electromagnetic wave absorbent has the characteristics that the absorbing strength is high at low thickness, and the frequency band of effective absorbing is broad; the excellent wave absorbing property is realized. The preparation method has the advantages that the technology is simple, the cost is low, the complicated synthesizing equipment is not needed, and the hypertoxic organic solvent is not needed.