The invention discloses a method for co-processing fly ash and chromic slag. In the landfill process, through the special biochemistry and engineering measures, fly ash and chromic slag are subjected to harmless treatment. In the method, fly ash and chromic slag are transferred into a storage yard, an anti-seepage layer is laid in the storage yard, a flow guide material is laid at the bottom, and a mixing layer of biogas slag, a carbon source, ferrous sulfate, nutritional additives, fly ash and chrome slag is laid on the upper portion; an inner electrolytic ceramsite layer is placed on the upper portion of the mixing layer. In the running process, a carbon source solution is injected from the upper portion of the storage yard irregularly, percolate is collected into a percolate collection system irregularly through a bottom flow guide material, and the percolate flows back to the top of the storage yard for spraying and recharging.