Abstract: This review introduces the role of brassinolide in promoting plant growth and raising the yield of crops and recounts its physiological basis in brief. Comparing the difference in the modes of action between brassinolide and auxin, gibberellin, it has been proposed that the signal transduction pathway of BR is different from tho se of other plant hormones. Moreover, the article discusses the mechanism by which promotes plant growth in detail by analysing the cell morpho genesis, expansion of cell wall and the cole of cytokeloton in cell elongation.