In this work, the intergranular insulated Fe/SiO2 soft magnetic composite cores with tunable insulating layer thickness were prepared by a modified Stober method combined with the spark plasma sintering technology. Most of the conductive Fe particles could be coated uniformly by insulated SiO2 using the modified Stober method, and the high compact and intergranular insulated cores could be obtained quickly by the spark plasma sintering process. The intergranular insulated Fe/SiO2 composite cores exhibited much higher electrical resistivity, lower core loss, better frequency stability of permeability and large higher quality factor than that of raw Fe core without insulated SiO2. The thickness of SiO2 insulating layer, electrical and magnetic properties of intergranular insulated Fe/SiO2 composite cores could be readily controlled by adjusting the tetraethyl orthosilicate concentration. The thickness of SiO2 insulating layer and resistivity of Fe/SiO2 composite cores first increased and then dropped with increasing the tetraethyl orthosilicate concentration, while the permeability and core loss changed in the opposite direction. Fe/SiO2 composite core showed the optimal performance when the tetraethyl orthosilicate concentration was 0.135 mol l(-1), which exhibited better frequency stability at high frequencies, much higher electrical resistivity, higher quality factor and lower core loss.