Pure iron with C/Si > 1 and C/Si < 1 was smelted by a vacuum arc furnace, and the grain size was controlled through different heat treatments. The microstructure of pure iron was observed by using an optical microscope, and the grain size was subsequently measured and calculated. Finally, the coercive force, saturation magnetic induction, and permeability were measured using a vibrating sample magnetometer. The results indicate that the coercive force increases with decreases in the average grain diagonal size. An increase in the uniformity of the grain increases the saturation magnetic induction. The permeability depends on the average grain diagonal size and the uniformity of the grain as well as the chemical composition of pure iron.