This invention discloses a method for preparing cleaning agent for printing ink on plastic surface. The cleaning agent comprises: organic diluting agent 40-55 parts, organic ester 27-38 parts, ketone 15-23 parts, and nonvolatile component 1-3 parts. The method comprises: dissolving organic ester and ketone in organic diluting agent, mechanically stirring uniformly, then adding nonvolatile component, and mixing uniformly to obtain colorless and transparent cleaning agent. The cleaning agent has such advantages as high selectivity, good cleaning effect, and low solvent volatility, no matrix softening, low toxicity, low harm to human bodies, and simple formula, and can be used for cleaning printing ink on the surface of plastic plate or mackintosh surface, especially the surface of soft plastic package.