The invention discloses a styrene-acrylic emulsion and a synthetic method thereof and an electrical steel coating. The styrene-acrylic emulsion comprises the following components in percentage by weight: 10.0-30.0% of styrene, 10.0-30.0% of butyl acrylate, 1.0-5.0% of 2-ethylhexyl acrylate, 0.5-2.5% of methyl methacrylate, 0.3-1.0% of methacrylic acid, 0.1-1.5% of alkyl phenol polyoxyethylene ether OP-10, 0.1-2.0% of sodium dodecyl sulfate K12, 0.1-1.0% of N-methylolacrylamide, 40.0-70.0% of water, 0.2-2.0% of sodium bicarbonate, and 0.2-2.0% of ammonia persulfate. A preparation method comprises the steps of firstly preparing pre-emulsion and initiator water solution, and mixing and emulsifying the pre-emulsion and initiator water solution in batches. The styrene-acrylic emulsion is narrow in particle size distribution, and fine in particle size; the prepared electrical steel coating is good in resin dispersibility, long in painting liquid shelf life, and suitable for high-speed roller painting.