Abstract: In order to explore the effects of potassium humate application on the growth of Populus in different periods, Populus in Hexi area of Gansu Province were taken as the research object, and the tree height, DBH and basic wood density of Populus after applying potassium humate fertilizer in different periods were investigated and compared. The results showed that under three different topdressing methods, the tree height, DBH and basic wood density of Populus seedlings after 1 year were significantly higher than those without fertilization treatment. The trees treated with fertilization in April and October were the highest in height（7.17 m）, the largest in diameter at breast height（8.02 cm）, and the basic density of wood was relatively high（0.38 g/cm~3）, which was the best fertilization method in this experiment.