The invention discloses a water-based nano thin-coating heat preservation paint and a preparation method thereof. The paint comprises the following raw materials by weight: 30-40 parts of an acrylic emulsion, 5-10 parts of titanium dioxide, 20-40 parts of hollow glass beads, 5-20 parts of aerogel and 5-10 parts of a film-forming assistant. According to the invention, the hollow glass beads and aerogel are used as the heat insulation basic raw materials, the heat conductivity coefficient of the paint is greatly reduced and is as low as 0.031-0.035W/m.K, and the paint can reach a remarkable heatinsulation effect under the condition of a very small construction thickness. Meanwhile, the hollow glass beads and the aerogel are conducive to improving the chemical stability of the paint itself,thus improving the covering power, lightening power, corrosion resistance, light resistance and weather resistance, and enhancing the mechanical strength of the paint; cellulose, a wetting dispersant,a defoaming agent and a preservative are mixed; by virtue of ethylene glycol, the acrylic emulsion and a pH regulator, the paint has excellent cohesiveness, weather resistance, film-forming properties, gloss and color retention and mechanical properties; and the use of a vinyl chloride-vinylidene chloride copolymer emulsion also can reach a grade A1 flame retardant effect.