The invention discloses a hierarchical structure wave absorbing agent and a preparation method thereof. The wave absorbing agent is composed of a ternary compound and a film former, the ternary compound is of a hierarchical coated structure and contains a binary metal oxide, RGO and MnO2, the RGO is coated outside the binary metal oxide, and the MnO2 is coated outside the RGO. The binary compoundis a magnetic loss medium, and the RGO is a dielectric loss and conductive loss medium. The wave absorbing agent not only integrates magnetic loss with electrical loss, but also greatly enhances interface polarization of the compound on electromagnetic waves through the design of the hierarchical ordered coated structure. The outermost MnO2 is not only conducive to incidence of electromagnetic waves, but also can effectively reduce direct reflection of the RGO on the electromagnetic waves, and further enhances the wave absorbing performance of the compound.