The invention relates to an intergranular insulated high-silicon electrical steel core and a preparation method thereof. According to the technical scheme, iron-silicon alloy powder, absolute ethyl alcohol, a silane coupling agent and distilled water are sequentially added into a reaction container according to the mass ratio of iron-silicon alloy powder, absolute ethyl alcohol, the silane coupling agent and distilled water of 1: (6-10): (0.04-0.1): (0.2-0.5) and then are stirred; tetraethoxysilane or tetramethoxysilane is added, ammonium hydroxide is added, and stirring is continuously performed; a mixture is washed, filtered and dried; the mixture is kept warm for 1-3 hours at the temperature of 600 DEG C to 800 DEG C and is cooled with a furnace and subjected to press forming; and a product is placed in a sintering furnace to be sintered for 1-10 hours at the temperature of 950 DEG C to 1,350 DEG C and is cooled with the furnace, and the intergranular insulated high-silicon electrical steel core is obtained. The intergranular insulated high-silicon electrical steel core and the preparation method have the characteristics of simple process, short period, high material utilization rate and low cost, and the prepared intergranular insulated high-silicon electrical steel core is low in loss, good in stability and long in service life.