Abstract: Effect of the pesticide on the chlorophyll in the Hydrangea was studied by using the spray treatment. The results showed that the content of chlorophyll displayed the characteristics of increasing at first and decreasing later on. And the change of the content of chlorophyll showed some time effect along with the prolongation of the time at the three days after it was treated by chlorothalonil. Compared with the control(CK), the content of the chlorophyll a and b in the Hydrangea treated with 1 200 mg/kg chlorothalonil increased significantly by 151.60% and 156.76%, respectively. The significant differences between the different pesticides were not found. Study showed that the change in chlorophyll content of hydrangea was related to pesticide concentration, not concerned with pesticide varieties.