The invention discloses a preparation method of a double-faced compound warm-keeping and energy-saving wallboard. The method comprises the following steps of mixing and stirring 50-70% of bottom ash of household garbage after the household garbage is burnt to generate electricity, 5-20% of milling fine sand, 5-15% of lime and 5-20% of water by mass percentage, obtaining hard slurry, injecting the hard slurry into a panel mold, placing a corresponding wire mesh, conducting three rolling procedures, steaming by high pressure, cooling, demolding, obtaining a panel, fixing the prepared panel on the two sides of a mold, mixing and uniformly stirring 30-50% of the bottom ash of the household garbage after the household garbage is burnt to generate the electricity, 10-20% of the lime, 10-25% of the milling fine sand, 10-20% of cement, 2-4% of plaster, 0.01-0.06% of aluminum powder and 5-20% of the water by mass percentage, obtaining slurry, injecting the slurry into a wallboard mold, stewing, steaming by the high pressure, cooling, demolding, and obtaining the wallboard.