The purpose of the invention is to provide a preparation method and an application of polylactic acid-glycolic acid copolymer coated by manganese dioxide layer, so as to solve the problem that the existing antineoplastic drugs are of poor biocompatibility, great toxicity and bad application effect. The preparation method comprises steps of weighing 100-200mg of 2-(N-morpholine) ethanesulfonic acid-water, adding it into 200-400mg of polylactic acid-glycolic acid nanometer particles, dissolving by ultrasonic wave for 5min under conditions of power of 40-100W and temperature of 25 degrees centigrade, then adding 3.0-5.0mL of potassium permanganate solution whose concentration is 5.0M, reacting for 30min, thereby obtaining the polylactic acid-glycolic acid copolymer coated by manganese dioxide layer. The preparation method of polylactic acid-glycolic acid copolymer coated by manganese dioxide layer has simple process, low production cost, high output and small toxicity and side effects; the polylactic acid-glycolic acid copolymer coated by manganese dioxide layer has a good inhibition effect to the amplification of tumor cells, and has good economical and social benefits.