As one of the core materials for magnetic devices, NiZnCo ferrite has excellent magnetic properties. However, the current magnetic devices are moving toward miniaturization and high performance, so the research of NiZnCo ferrite in the middle- and high-frequency bands is necessary. Here, Ni0.42Zn0.53Co0.05Fe1.94O3.91 + 0.5 wt% Bi2O3 + x wt% Y2O3 (NZCBY, x = 0–0.5) ferrites are prepared by solid phase reaction method. The improvement of the microstructure and electromagnetic properties of the material by doping Y2O3 is explored in detail. The right amount of Y2O3 can refine the grains and increase the density to 5.151 g/cm3. In terms of magnetic properties, the Y2O3 can reduce the saturation magnetization of the ferrite, and the coercivity decreases to 153.75 A/m when the doping amount x = 0.1. The cut-off frequency and Q value in the frequency range of 1–30 MHz are significantly increased. In addition, the AC resistivity of the NZCBY ferrite at 6.78 MHz is increased from 3.75 × 103 Ω∙m (x = 0) to 8.63 × 103 Ω∙m (x = 0.3). This work contributes to the development of materials for high-frequency passive devices and has the opportunity to be applied to the field of wireless charging.