The invention discloses a protective device applied for sterilization and bacterial infection prevention of municipal greening seedlings, wherein the protective device comprises a coating device for whitening trees and a supply device for supplying a material to the coating device; the coating device comprises a sleeving mechanism for sleeving the exterior of a tree, and a coating mechanism for whitening the tree sleeved by the sleeving mechanism, and a power supply mechanism for providing driving power to the coating mechanism; the power supply mechanism comprises an auxiliary power source for providing a power source; the supply device comprises a liquid storage mechanism, a stirring mechanism, a pump material conveying mechanism and a support-conveying mounting frame, and a mounting frame body is provided with a main power source, and the main power source provides driving electric energy for the stirring motor and a pump body; a charging wire is arranged between the main power source and the auxiliary power source, and the main power supply is used for charging and recharging the auxiliary power source.