The invention discloses an automatic smearing device for forestry tree planting. The automatic smearing device is composed of moving wheels, a supporting bottom plate, a parallel moving mechanism, a storage battery, a lifting mechanism, a first smearing mechanism, a second smearing mechanism, a storage bucket, a pressure pump, a supporting frame, a first feeding pipe, a second feeding pipe, a control switch and handles; the pressure pump is installed in the storage bucket, the storage battery is placed on one side of the storage bucket to provide power for the pressure pump, one end of each ofthe first feeding pipe and the second feeding pipe is installed in the storage bucket and connected with the pressure pump, and the other end of each of the first feeding pipe and the second feedingpipe is installed on the upper portion of a storage tank; and the lime paste in the storage bucket is gradually transported into the storage tank, and the lime paste in the storage tank flows into a smearing part through a discharging hole so as to smear the surfaces of the trees. The automatic smearing device has the beneficial effects that the surfaces of the trees can be automatically smeared,the smearing efficiency is greatly improved, the work burden is relieved, and the automatic smearing device is simple in structure, convenient to operate, high in adjustability and suitable for the smearing work of the trees of different diameters.