Abstract: Rhododendron hybridum was chosen as subjects and treated by different concentration of gibberellin（GA3），paclobutrazol（PP333），and dami-nozide（B9）. Their flower buds formation was observed and the concentration of endogenous hormones，i. e. zeatin（ZT），gibberellin（GA3），3-indole acetic acid（IAA）and abscisic acid（ABA）in the buds were detected. Experiment results showed that GA3 had a significant promotion of the plant’s florescence，while PP333 and B9 delayed the florescence and B9 increased its tidiness substantially. External GA3 treatment stimulated the endogenous GA3，reduced the concentration of IAA and ABA，and increased ZT concentration followed by a decrease of ZT. Both B9 and PP333 could reduce the concentration of GA3，ZT and IAA while increase ABA concentration. The results indicated that the flowering period can be promoted by high concentration of ZT and GA3 and low concentration of ABA during flower bud shape differentiation.

Key words: Rhododendron hybridum, plant growth regulator, flowering time regulator, endogenous hormone