The invention provides a thick coating material capable of purifying air and a preparation method thereof, belonging to the building material field. An internal wall coating decorative material comprises 5 to 40 weight portions of a porous absorbing material and 10 to 40 weight portions of a composite photocatalysis material in every 100 weight portion of the paint. In the preparation method, the coating material, is formed by compounding a mineral material with the nanometer photocatalysis material to obtain a high activity purifying material, matching the high activity purifying material with other nanometer materials and the porous absorbing material, and then adding an inorganic filling material, a skeletal material and other addition agents, can remove harmful gases such as formaldehyde and toluol in air and has the environmental protection function. The paint has good effect for removing formaldehyde, is effective continuously, has certain thickness when the coating layer is used, has simple construction, and beautiful and elegant patterns, is well-bedded, is strong in the three-dimension effect and has good decorative effect.