Mix magnesium oxide powder plant powder or mineral powder in a predetermined mixing ratio to obtain a mixture; add water to the mixture to obtain a moist powdered mixture; embed the moist powdered mixture into the molding machine In the frame mold device, the mold device consists of a frame mold 3 and a preheated lower mold 2. The upper mold 1 is used to heat and compress the moist powder mixture to harden the mixture; finally, the resulting product is released from the mold. The advantages of this method are that the building materials have good strength and are flame retardant and do not release toxic gases when burned. Since the building materials can be manufactured through injection and extrusion molds, they can be manufactured on a commercial scale at low cost.