Red mud foam lightweight thermal insulation material was prepared by red mud, fly ash, cement as main raw materials, adding a certain amount of adhesive, through ingredients, mixing, molding, foam, sintering process. The influence of the ratio of red mud and fly ash on the properties of materials was studied and the mechanism of influence was analyzed. The test results show that performances of the samples were best when the ratio of red mud and fly ash is 5:4 and its flexural strength is 0.44MPa, compressive strength is 1.23MPa, density is 481kg/m3.