The invention discloses a method for reducing viscosity of residue on evaporation from distillation recovery of a polymerization solvent NMP for producing PPTA. The method is as below: neutralizing a mixed mother liquor containing NMP with alkali, adding composite salt, and conducting coarse steaming and concentration to dryness to obtain pie-shaped residue, wherein the composite salt comprises sulfate and calcium salt; conducting rotary drum evaporative desalination on the pie-shaped residue after coarse steaming and concentration; and isolating salt slag and NMP for refining. The method improves the viscosity of a NMP-water-CaCl2 multicomponent system, reduces the adhesiveness of CaCl2 residue on evaporation in the wall, and avoids the formation of high-viscosity NMP-water-CaCl2 ternary complex adhered to the inner surface of the evaporator and tube wall of a heat exchanger in the evaporation recovery of NMP solvent, so that the multi-effect evaporation process for distillation recovery of NMP solvent can be conducted continuously, stably and efficiently.