The invention discloses a 
fly ash washing process for multistage reverse pulping of 
carbon dioxide tempering. The 
fly ash washing process comprises the following steps that 1, 
fly ash and water are mixed according to the 
solid-to-
liquid ratio of 1: (3-5) to prepare 
slurry, and meanwhile, 
carbon dioxide gas is introduced into the 
slurry to adjust the pH value to be 6-8; 2, suction 
filtration is conducted on the 
slurry to obtain high-concentration 
water washing liquid and 
solid residues; 3, the 
solid residues obtained in the previous step are mixed with water according to the solid-to-
liquid ratio of 1: (3-5) to prepare slurry; 4, suction 
filtration is conducted on the slurry prepared in the step 3 to obtain high-concentration 
water washing liquid and solid residues; 5, the third step and the fourth step are sequentially repeated once, and high-concentration washing liquid and solid residues are obtained; 6, the solid residues obtained in the step 5 are mixed with water according to the solid-to-
liquid ratio of 1: (5-8) to prepare slurry; and 7, the slurry prepared in the step 6 is subjected to suction 
filtration, low-concentration 
water washing liquid and solid residues are obtained, the low-concentration water washing liquid is concentrated through a DTRO membrane, concentrated water and 
fresh water are obtained, the concentrated water is reused in the step 1 for preparing the slurry, and the 
fresh water is reused in the step 6 for preparing the slurry.