The invention discloses an expanded type fireproof coating and a preparation method thereof, which are characterized by comprising the steps of grinding and dispersing 15-35 percent of microcapsule flame retardants, 5-10 percent of fillers and 10-30 percent of solvent according to the percentage of the total mass of the coating after preparation until the fineness thereof is less than 90 microns;then adding and dispersing coating matrixes and additives which respectively take up 20-40 percent and 1-5 percent of the total mass of the coating after preparation until the system is uniform; and alternatively adding flame retardant synergist agents which account for 0-10 percent of the total mass of the coating after preparation before grinding. The obtained expanded type fireproof coating has good stability, overcomes the defects of poor high-temperature resistance, poor anti-aging performance, poor water resistance and the like in the traditional organic expanded type fireproof coating,lowers the use amount and cost of the flame-retardant additives which all realize non-halogenation, does not cause larger impact on the environment, and has very good application prospects.