The invention discloses a nano flame-resistant concrete protective coating and a preparation method thereof, wherein the protective coating comprises the following ingredients in parts by weight: 55-75 parts of modified nano-silica sol emulsion, 8-10 parts of attapulgite whiskers, Schiff base modified 3-5 parts of non-toxic graphene compound, 0.2-0.5 parts of wetting and dispersing agent, 0.2-0.5 parts of thickener, 0.2-0.5 parts of defoamer, 1-3 parts of leveling agent, 25-35 parts of deionized water . The preparation process is as follows: mix the modified nano-silica sol emulsion, attapulgite whiskers, and Schiff base modified graphene compound according to the above protective coating formula, and use a high-speed disperser to stir and disperse at high speed for 30-60min; then the above protective coating Add the remaining wetting and dispersing agent, thickener, defoamer, leveling agent, and deionized water to the formula; adjust the state of the high-speed disperser to medium-speed stirring and dispersing, continue stirring evenly, and then filter and pack. The protective coating provided by the invention has good physical and chemical properties such as alkali resistance, water resistance, weather resistance, adhesion, fire resistance and the like.