The invention provides a root invasion-proof degradable masterbatch for a water dropper. The masterbatch is prepared from high-density polyethylene, polylactic acid-copper nanometer microcapsules and oxidized polyethlene wax. The invention further discloses polylactic acid-copper nanometer microcapsules and a preparation method for the masterbatch, wherein polylactic acid is capable of providing an acidic environment for the generation of bivalent copper ions during a degradation process, thus overcoming the problem that a copper root removal technology cannot be realized in case of the insufficiency or the lack of a plant acid under the constraint of a soil environment; the water dropper prepared from the masterbatch has a great root invasion-proof effect.