The invention discloses a harmless treatment method for arsenic-iron residue. The harmless treatment method comprises: uniformly mixing arsenic-iron residue, cement and polyvinyl alcohol ammonium phosphate, adding water, stirring, injecting into a mold, molding, curing, and demolding. According to the present invention, preferably polyvinyl alcohol ammonium phosphate and cement are used as the curing agent, and synergistically act, such that the obtained arsenic residue solidified body has high stability and low compatibilization ratio; and the solidified product is detected according to toxicity characteristic leaching procedure (TCLP), and the results show that the toxicity leaching concentrations of arsenic and other harmful elements in the leaching solution are far lower than the limits specified in the Identification standards for hazardous wastes-Identification for extraction toxicity GB 5085.3-2007, such that the product can be stored and landfilled.