The invention discloses a lightweight energy-saving paint and its preparation method. The paint provided by the invention comprises the following components of: by weight, 45-55 parts of corundum hollow spheres, 20-30 parts of a lightweight filling material, 5-10 parts of fiber, 15-20 parts of a binder and 0-5 parts of an additive. The lightweight energy-saving paint prepared in the invention has characteristics of good fluidity, high strength, low thermal conductivity, strong adhesive force, high refractoriness, good chemical stability, strong corrosion resistance and the like, can be used for the surface coating of high temperature pipelines, thermal equipment and hearth inside and outside parts to effectively inhibit heat radiation and calorific loss, and can be used for spraying and coating the internal and external surfaces of various concrete structures and steel structure buildings so as to save energy, insulate sound and prevent fire.