Powder of nano Ni-Zn ferrite was doped with Co²⁺, Mn²⁺ and Cu²⁺ respectively with hydrothermal method, which then was characterized by means of XRD, TEM, and VNA in terms of the doping effect on the particle size, morphology, and electromagnetic wave absorption performance of the doped powders. Meanwhile, plain nanometer Co-Ni-Zn ferrite was also prepared by hydrothermal method for varying Co²⁺ content. Results show that after doping, the particle morphology changed from spherical one to irregular quadrilateral one with the average particle size 35~60 nm. The lattice constant also increases from 0.8404 to 0.8352 nm for Co²⁺ doping. The Co^{2 +} doping can change the position of the absorption peaks, increase the bandwidth of the absorber, and improve the performance of the materials in GHz low frequencies. The doping ratio of Mn²⁺ can affect the lattice constant of the nano Ni-Zn ferrite, but nano particles are easy to agglomerate, thus Mn²⁺doping exhibited negative effect on the absorbance performance. For the doping of Cu²⁺, particles are still apt to agglomerate, however, with a dopant dose of 0.15Cu²⁺(atomic fraction), the absorbing performance of nano Ni-Zn ferrite powder became better.