A method of producing an extremely thick insulation coating on a surface of an electrical steel, comprises the following steps: 1) preparing a coating liquid—stirring sufficiently the coating liquid for 0.1˜4 hours, with the viscosity of the coating liquid being within 10˜80 S; 2) coating a strip steel—using a double-roller or a tri-roller coating machine, wherein the film thickness and evenness can be controlled by adjusting different parameters; 3) baking the coating—using three sections, that is, a drying section, a baking section and a cooling section, to bake the coating, wherein the temperature in the drying section is 100˜400° C., the temperature in the baking section is 200˜370° C.; the time in the whole drying and solidification section is 33˜144 seconds, wherein the time in the drying section is 9˜39 seconds, and the baking time is 24˜105 seconds; wherein in the baking process, the strip steel having been coated is conveyed in a non-contact way, in particular, the strip steel is conveyed by blowing pressure-adjustable air onto the lower surface to make it float; the air pressure is 0˜2000 Pa; the wet film is kept out of contact with the furnace rollers before it is solidified, guaranteeing that the surface of wet film is intact; 4) online detecting the film thickness.