Abstract: In this study, the effect of the trisiloxane surfactant (Silwet408) on the physicochemical properties of pesticide solutions, and the internal relation between the behavior of single droplets of Silwet408 solution on rice leaf surface and the control effect on rice leaffolder, Cnaphalocrocis medinalis Guenée were explored. The change of surface tension, viscosity, pH value and maximum retention of chlorantraniliprole 200 g/L suspension concentrate(SC) diluent solution were determined. The leaf surface was characterized by OCG method. And the adhesion behavior analysis of single droplets on rice leaves was conducted according to leaf inclination angle. Field efficacy tests were also carried out. The results showed that the apparent surface free energy (SFE) values of the adaxial and abaxial rice leaf surface were 31.48 mJ/m² and 34.19 mJ/m², respectively. The leaf angles of the second and third leaves were relatively small and their respective average values were (11.09 ± 2.74)° and (19.98 ± 5.67)°, respectively, which indicated that the leaf shape of high inclination angle was not conducive to the adhesion of droplets on the rice leaves. The surface tensions of chlorantraniliprole 200 g/L SC 4 000 times and 5 000 times diluent solution were (44.64 ± 1.04) mN/m and (46.14 ± 0.62) mN/m, respectively, which were higher than that of the rice leaf apparent surface free energy. Their single droplets of those solutions rolled off rice leaves with the inclination angles of 79° and 70°, respectively. After the addition of Silwet408 adjuvant at the concentration of 125 mg/L, the surface tension of the solution was lower than that of therice leaf apparent surface free energy. Its single droplet of the solution adhered to rice leaf with inclination angles and the leaf became wetted. The maximum retention amount of the solution on the rice leaf was also significantly increased. The pH and viscosity values of chlorantraniliprole 200 g/L SC diluent solution had a little change with or without Silwet408 adjuvant. Field experiments showed that the protecting effect of leaves and the insecticidal effect of chlorantraniliprole 200 g/L SC 5 000 times diluent solution on C. medinalis were significantly improved 14 days after spray by adding Silwet408 adjuvant at the concentration of 125 mg/L. In a word, physicochemical properties of the spray solution could match with the characteristics of the rice leaf after adding Silwet408 adjuvant at the concentration of 125 mg/L, which could improve the control effect of chlorantraniliprole 200 g/L SC 5 000 times diluent solution against rice leaffolder.