The invention discloses a method for preparing toughening calcium carbonate composite powder for a sheet molding compound (SMC). The method comprises the following steps of: washing calcite raw ores, airing, and crushing; grading by a vibrating screen; mixing for preparing; wrapping; drying; and modifying The method has the advantages that compared with those of the ordinary product, the toughness of the toughening calcium carbonate composite powder which is produced by the method can be improved by more than 20 percent, and the contractibility rate can be reduced by 30 percent; and the curing performance, anti-aging performance and surface quality of products can be improved.