The invention relates to a flame-retardant thermal-insulating material for building. The flame-retardant thermal-insulating material comprises a backing reinforcement layer, a thermal insulation layer, a flame-retardant layer and a decoration layer, wherein a first elastic layer is arranged between the backing reinforcement layer and the thermal insulation layer, a second elastic layer is arrangedbetween the flame-retardant layer and the decoration layer, the thermal insulation layer is made of a radiation cross-linking polyethylene material, the flame-retardant layer comprises a vacuum flame-retardant plate, a rock wool layer and a reinforcement layer, a plurality of reinforcing ribs are arranged in the vacuum flame-retardant plate, the rock wool layer is a glass wool plate layer, the vacuum flame-retardant plate and the rock wool layer are adhered through an adhesive, and the rock wool layer and the reinforcement layer are adhered through an adhesive. According to the present invention, by arranging the first elastic layer between the backing reinforcement layer and the thermal insulation layer and arranging the second elastic layer between the flame-retardant layer and the decoration layer, the collision resistance and the deformation resistance of the thermal insulation plate can be improved.