In this paper, three kinds of organic/inorganic hybrid flame retardant coatings were prepared by sol-gel method using water-based nano-aluminum sol as the inorganic component (ALS), methyltriethoxysilane (MTES) and phenyltriethoxysilane (PhTES) as the organic precursors. The three kinds of coatings are nano-aluminum sol hybrid methyltriethoxysilane (ALS/MTES), nano-aluminum sol hybrid phenyltriethoxysilane (ALS/PhTES), and nano-aluminum sol hybrid methyltriethoxysilane and phenyltriethoxysilane (ALS/MTES/PhTES). The flexibility test of the coatings showed that the flexibility of ALS / PhTES and ALS / MTES / PhTES coatings containing phenylsilane were better than that of ALS / MTES coatings, indicating that the addition of PhTES could improve the flexibility of the coating. The thermal stability test of the coatings illustrate that the Tg of ALS/MTES/PhTES coating is 205.78°C, which is the highest, besides, the residual mass reaches 72.57% when the temperature is 900 °C. It illustrates that the addition of PhTES promotes the thermal stability of the coating in some extent. The SEM figure of the samples show that the surface of coating is uniform, dense and without obvious phase interface. Otherwise, the XRD test results of the coating before and after ablation show that its mechanism of fire-resistant is attributed to the decomposition of boehmite (AlO(OH)), random depolymerization of the main chain Si-O-Si in coating and the decomposition of side chain alkyl.