Abstract: In order to evaluate key factors affecting the effective deposition of pesticide droplets on tobacco leaves during pesticide spray, so as to improve disease control efficiency and reduce pesticide pollution, parameters such as critical surface tension, point of runoff (POR) and maximum retention (R_m) on mature tobacco leaves at different spray distances and leaf inclination angles were measured by the Canny edge detection algorithm, Zisman method and micro-weighing detection method. The results showed that: 1) There was a significant negative correlation between the surface tension of pesticide liquid and the cosine values of the contact angle. The critical surface tension of mature tobacco (cv. Honghuadajinyuan) leaves was 31.44 mN/m. 2) The inclination angles of upper leaves were larger and mainly in the range of 60°-70°, while those of lower leaves were smaller and mainly in the range of 20°-40°, and those of middle leaves were mainly in the range of 50°-60°. 3) POR and R_m values were affected by the leaf inclination angle and spray distance. The differences of POR among different leaf inclination angles were quite big and reached 30%-43%. POR significantly negatively correlated with the leaf inclination angle. With the mean value of about 28 μL/cm², POR was the highest at the spray distance of 50 cm and the leaf inclination angle of 20°-30°, which was nearly 50% higher than that at other distances. POR and R_m values changed slightly at spray distances larger than 100 cm. The POR and R_m of leaves with inclination angles of 40°-70° basically remained unchanged at different spray distances. Therefore, additives were necessary during spraying pesticides on tobacco leaves for reducing the surface tension of pesticide droplets to a level lower than the critical surface tension and for promoting the wetting and spreading abilities of the sprayed pesticides. The recommended spray distance for lower leaves was larger than 100 cm, and those for middle and upper leaves were larger than 50 cm, and the application dosage of pesticide should be lower than the POR.