Abstract: NiCuZn soft magnetic ferrite was prepared by solid state sintering with raw powder of different particle size prepared by changing the secondary ball milling time (1-6 h). The effect of the particle size on the microstructure and magnetic properties of the soft magnetic ferrite was studied. The results show that the powder particle size decreased with the extension of secondary ball milling time, and the size distribution gradually concentrated. The uniformity of grain size of soft magnetic ferrite prepared became better and then worse, and the grain boundary became clear and then blurred. With the decrease of the powder particle size, the initial permeability, saturation magnetic induction intensity, relative density and resistivity of the soft magnetic ferrite increased first and then decreased, and the power loss decreased first and then increased. When the secondary ball milling time was 3 h, the powder partide size was mainly between 2.5-3.5 μm, with average particle size of 3.237 μm. At this time, the grain boundary of the prepared soft magnetic ferrite was relatively clear, and the grain size was relatively uniform. The initial permeability and saturation magnetic induction intensity reached the maximum value of 1385 H·m^-1 and 360 mT, respectively, and the power loss reached the minimum value of 284 kW · m^-3.