The modified desulfurized ash is prepared through autoclave curing the desulfurized ash for 6 h at 175.4 oC in the presence of 2.0 wt% Fe2O3 and 0.75 wt% H2O2. In this process, 47.64 % of the calcium sulfite in the desulfurized ash is converted into calcium sulfate. The autoclaved brick is made by 36 wt% modified desulfurized ash, 24 wt% fly ash, 32 wt% sand and 8 wt% stones. The water-solid ratio is 0.10. The compressive strength of the brick is up to 15.7 MPa. For this method, the calcium oxide and calcium sulfate in the modification desulfurized ash are used to replace the lime, gypsum and other materials. The solid wastes are reused and natural resources are saved.