The invention relates to the field of building material, in particular to a low-cost electromagnetic wave-absorbing materials; specifically, the invention provides a low-cost and high-performance high iron pulverized ash cement-based composite wave-absorbing material applied to buildings, comprising dry material and water; wherein, the dry material comprises cement and high iron pulverized ash, the weight ratio of the cement to the high iron pulverized ash is 60-70: 30-40; water to the dry material 0.30-0.40:1; calculated by the content of Fe2O3, the content of the Fe component content in the high iron pulverized ash is more than 15%; the invention also provides the preparation method for the high iron pulverized ash cement-based composite wave-absorbing material applied to buildings, comprising the following steps: 1) dryly mixing the dry material evenly; 2) adding water to the dryly mixed dry material and mixing the mixture evenly; 3) pouring the mixture obtained in step 2) into a steel mould and moulding by vibration; 4) demoudling after moulding and carrying out maintenance under standard curing conditions.