The invention relates to the field of carton processing equipment, and particularly relates to a flattening device suitable for carton processing. The flattening device comprises a base, a housing, anash removing structure, flattening structures, a first height adjusting structure, an auxiliary structure, a second height adjusting structure, a flattening structure and a reset structure, wherein the housing is provided with the ash removing structure, then waste scraps on a carton can be conveniently removed and stored through the ash removing structure, the situation that the waste scraps arepressed on the carton, and consequently the carton deforms and even is damaged is effectively avoided, and then the flattening efficiency and quality of the carton are greatly improved; the first height adjusting structure is provided with the flattening structure used for flattening the carton, the housing is provided with the flattening structures in one-to-one correspondence with the flattening structures, tension can be conveniently applied to the carton through the flattening structures before the carton is flattened, the carton bears lateral tension, and the function of preliminarily resetting the wrinkle position is achieved; and meanwhile, through cooperation of use of the flattening structures, secondary wrinkles are effectively prevented, and the flattening efficiency and quality of the carton are improved.