The invention discloses a fireproof coating and a preparation method thereof, and relates to the field of coatings. The fireproof coating provided by the invention comprises the following components in parts by weight: 180-250 parts of an acrylic emulsion, 30-50 parts of potassium silicate, 400-450 parts of a fire retardant, 50-70 parts of chlorinated paraffin, 20-30 parts of diantimony trioxide, 5-10 parts of nano-magnesium hydroxide, 10-30 parts of composite zinc phosphate, 5-10 parts of titanium dioxide, 10-15 parts of mica powder, 2-6 parts of a dispersing agent, 1.5-2.5 parts of a de-foaming agent, 5-15 parts of a film-forming aid, 1-3 parts of a leveling agent, 20-30 parts of a thickening agent, 1 part of an anti-mould and anti-alga agent and 120-200 parts of de-ionized water. The coating belongs to environment-friendly coatings, is long in fireproof time, good in decorative performance, excellent in waterproof performance and free from APEO (alkylphenol ethoxylates) and compounds of metal such as lead or chromium, and cannot cause harm to environment and human health.