Abstract: The stem growth of cut_flower rose (Rosa hybrida) was observed on 3 cultivars in different seasons, and the effect of GA3 on stem(flower branch) elongation was studied. The results showed:(1) The relations between growth time and the length of the stem could be expressed by Logistic equation　［y=K/(1+eA+Bt)］, and correlation index (R2) was more than 0.978. (2)The peak time in the growth speed of flower branch was when the alabastrum appeared.(3)The growth regularity of stem was changed by GA3 treatement, and the stem elongation was promoted and the length increased by 22.5%-63.1% with 100 mg/L GA3. Moreover,it was on the period of alabastrum appearance that the GA3 effect was best.