The invention provides a magnetic core preparation method. The magnetic core preparation method comprises the following steps of preparing a master alloy, and smelting the master alloy at a certain temperature and time by utilizing a vacuum induction furnace to cast a master alloy steel ingot; re-melting the master alloy steel ingot in a medium-frequency induction furnace at a certain temperature, and preparing an amorphous strip in the non-vacuum environment by utilizing a single roller rapid quenching method; rolling the amorphous strip into a magnetic core and carrying out horizontal heat treatment, wherein the amorphous strip comprises the components by atom number percent and the chemical component expression of the amorphous strip is FeSiB. Starting with the component design, smelting link and heat treatment link in the strip preparation process, the amorphous strip with good quality is prepared, and horizontal magnetic heat treatment is carried out on the ferromagnetic core prepared by rolling the strip on the basis of the amorphous strip, thus obtaining an inductance magnetic core with constant magnetic permeability.