Alkaline nano-silica sol was grafted and modified by KH560 and composite with styrene-acrylic emulsion to prepare film base material. Then, two kinds of color thermal insulation and energy saving coatings were prepared by adding rutile type titanium chromium yellow and corundum type chromium green color paste respectively. The energy saving performance and heat insulation mechanism of the composite coating were investigated under the conditions of different functional pigment types and dosage. The results show that the average particle size of silica sol is reduced from 987.3nm to 72.3nm, the absolute value of Zeta potential is increased by 29.7 eV, and the dispersion of silica sol in styrene-acrylic emulsion is improved. When the content of Ti-Cr yellow and Ti-Cr green were 20% and 10%, the thermal insulation performance of the two kinds of color coatings reached the best, the solar reflectance was 0.633 and 0.484, the infrared emissivity was 0.91 and 0.90, and the equilibrium temperature was 6.6℃ and 4.8℃ lower than that of the blank test plate, respectively. At the same time, the two kinds of color coatings had good mechanical properties and corrosion resistance.Key words: Mechanism of heat insulation ;Modified silica sol; Styrene-acrylic emulsion; Composite coating; Thermal insulation and energy saving coating; Reflective pigment