Abstract: In order to investigate the effect of GA on emasculation and Chlorophyll of sunflowers ,five different concentrations of GA3 and two sunflowers were used as materials, which were fertile inbred lines 9D002 and sterile lines 121010. The results showed that all five different concentrations of GA3 reduced the pollen viability, with utilized of 0.015 mg/g, 0.025 mg/g, 0.035 mg/g, 0.045 mg/g, 0.055 mg/g GA3. Pollen viability depressed less than 50% under the treatments of 0.035mg/g and 0.045 mg/g. More over, Chlorophyll content of plants was become lower than the control trial after GA3 treatment, and with the most significant decline under 0.035mg/g treatment. However, the outcrossing rate of inbred lines 9D002 was lower than sterile lines 121010. Furthermore, the outcrossing rate of sterile lines 121010 was 24.499 %, which was the lowest with utilized of 0.035mg/g GA3. In summary, it was the initial view that 0.035 mg/g GA3 might have a better effect on Emasculation of sunflowers.