The invention belongs to the technical field of baking-free bricks, and provides a red mud baking-free brick used for building and a preparation method. According to the baking-free brick, red mud andpolyaluminum chloride waste residues are used as main ingredient raw materials, and meanwhile, sludge aggregate, stone powder, ferric sulfate, modified arsenic rock, kaolin powder, zeolite powder anda diagenesis agent are added to prepare the baking-free brick. According to the red mud baking-free brick used for building and the preparation method, the red mud is adopted as the main raw material, so that stacking of the red mud is reduced, appropriation of land is reduced, land resources are saved, alkali in the red mud is prevented from permeating into the ground to cause underground waterand soil pollution, red mud dust flying with the wind is reduced, atmospheric pollution is reduced, and the ecological environment is protected.