The invention discloses a construction waste reclaimed thermal insulation brick. The brick is prepared from raw materials in percentage by weight as follows: 55%-85% of construction waste reclaimed material, 8%-15% of cement, 1%-5% of quicklime, 2%-15% of modified diatomite, 1%-8% of lignocellulose and the balance of water. The invention also provides a preparation method of the construction wastereclaimed thermal insulation brick. The method comprises the steps as follows: (1) stirring the construction waste reclaimed material, the quicklime, the lignocellulose and the water to obtain a mixture A; (2) adding the modified diatomite and the cement to the mixture A obtained in step (1), and stirring the mixture to obtain a mixture B; (3) pouring the mixture B obtained in step (2) in a prefabricated mold, performing cutting after initial setting, and carrying out curing and drying to prepare the construction waste reclaimed thermal insulation brick. Compared with the prior art, the construction waste reclaimed thermal insulation brick has high strength and low shrinkage, solves the problems of wall cracking, bubbling and the like of self-thermal insulation materials in use and has aformaldehyde adsorption effect.