Abstract: The surface free energy (SFE) of apple leaf, as well as the surface tension, static contact angle and dynamic contact angle in 0-60 s of diluted solution of 2.5% beta-cyfluthrin emulsion in water (EW) on apple leaf surface were determined by using optical contact angle measuring device.The results showed that the SFE value of the adaxial surface of apple leaf was about 52.76 mJ/m2, and the polarity component was dominant; while the SFE value of the abaxial surface was about 21.79 mJ/m2, and the dispersion component was dominant. The surface tension of 2 000-fold dilution of 2.5% beta-cyfluthrin EW on apple leaf was close to that of 3 000-fold dilution of 25 g/L beta-cyfluthrin emulsifiable concentrate (EC), but much lower than that of deionized water. There was no significant difference between the static contact angle of EW's 2 000-fold dilution and EC's 3 000-fold dilution, and the contact angle of EW's 2 000-fold dilution in 0-60 s declined the fastest. The results suggested that the adaxial surface of apple leaf was more wettable than the abaxial surface; when applied the 2.5% beta-cyfluthrin EW to apple trees, the best diluted solution was 2 000-fold.