Abstract: Applied the rare earth solution to Cunninghamia lanceolata and Populus ,the indexes about their roots assimilating rare earth were investigated. The observed results show that the average square differences on the total assimilating surfaces and the active assimilating surfaces of the young trees’ roots are remarkable, but the average square differences on the rates between the surface area and the volume of assimilating roots are not remarkable. When soaked by the rare earth solution of 500 mg/kg, the index of Populus roots assimilating rare earth is the highest; correspondingly, when sprayed by the rare earth solution of 800 mg/kg, the index of Cunninghamia lanceolata′s roots assimilating rare earth is the highest. Comparing to the CK, the growth of the height and the bottom diameter of the young tree and the dry weight of the root increased after treated by the rare earth solution.