The invention discloses a chemical foamed concrete and a preparation method thereof. The concrete product is prepared by using a cementing material, a foaming agent, a compounded additive and water as raw materials through a chemical foaming principle, and the added compounded additive realizes stable foaming speed stability, uniform bubble diameter and controllability. The chemical foaming preparation method has the advantages of simplicity, low production investment cost, and convenient construction. The foamed concrete product prepared in the invention has the advantages of fireproof property, waterproof property, sound insulation, heat insulation, light weight, high compressive strength and environmental protection. The bulk density, the compressive strength and the heat conduction coefficient of the obtained product are less than 400kg / m<3>, more than 3.5MPa and less than or equal to 0.07W / (M.K) respectively. The above formula adopting alkaline ash comprising alkaline furnace ashes, alkaline slag, alkaline furnace slag and other wastes as raw materials realizes comprehensive utilization of resources, changes wastes into valuables, and accords with the demands of sustainable development of national circular economy.