The invention discloses a residual active sludge dehydration filter aid and application thereof. The filter aid is selected from at least one of grafted puffed bagasse and sugarcane chaff. The filteraid provided by the invention can greatly improve the filter-press effect and efficiency, the water content of filter cake and the chemical oxygen demand (CODcr) of filtered liquid are lowered after dehydration, and the whole filter-press process is smooth, safe, easy in operation, needs simple equipment, and small investment, and has very good economical benefit and wide social benefit. The filter cake prepared by a dehydration method can be used for preparing a water body purifying material, so that the problem of residual active sludge in the sewage treatment process is transformed into a sewage treatment method, waste is changed into treasure, a closed loop is formed, and resource utilization of the residual active sludge is realized. The filter cake prepared by the dehydration methodcan also be used for preparing biological organic fertilizers, thereby realizing the resource utilization of the residual active sludge.