A producing method of an electrical steel extremely-thick insulating coating with a good film-forming property comprises the following steps that (1) adopted insulating paint is composed of, by weight, 10%-60% of organic resin, 28%-60% of inorganic color filler, 1%-15% of auxiliaries and solvents and the balance pure water; (2) surface treatment is conducted on a substrate, wherein surface modification treatment is conducted on the Fe-Si alloy substrate with the silicon content ranging from 1.5wt% to 3.0wt%, the surface of the substrate is covered with an oxidation film layer, and the surface roughness of the substrate is greater than or equal to 0.4 micron; (3) annealing is conducted, wherein the annealing temperature ranges from 780 DEG C to 1000 DEG C and is kept for 10 seconds-20 seconds, and the annealing atmosphere is a hydrogen and nitrogen gas mixture; (4) baking and curing are conducted, the baking process or the multi-band high infrared heating process or a combination of the baking process and the multi-band high infrared heating process is adopted. The film-forming property of the coating obtained with the method is excellent, and meanwhile the method has the advantages that the solid content required by the electrical steel environment-friendly extremely-thick insulating coating is high, surface insulativity and adhesiveness are excellent, and hot-pressing stability and corrosion resistance are good.