The invention relates to a coating and preparing method thereof, the purpose of the invention is to provide a composite silicon coating and preparing method thereof. The preparing method of the composite silicon coating includes steps: (1) organic silicane coupling agent and alkyl silicate of same mole are added into alcohol diluted solvent, mass of the alcohol diluted solvent is 1-100 times of total mass of the organic silicane coupling agent and the alkyl silicate; (2) inorganic acid and deionized water are added into the solution prepared by the step (1) to make pH of 1-5; (3) the solutionprepared by step (2) is painted on coating and composite silicon coating is obtained by natural drying. The prepared composite silicon coating is used as precoating before applying photocatalysis self-cleaning protective layer to the coating for obstructing and protecting bottom coating, is used for avoiding photocatalysis decomposition of organic film forming component in coating by titanium oxide, and is used for accelerating transition and combination of interface between bottom coating and titanium oxide self-cleaning protection layer.