Abstract: In order to improve the efficacy of glyphosate controlling alligator weed(Alternanthera philoxeroides), deposition characteristics of glyphosate droplets on alligator weed leaves were studied by means of detecting a tracer substance, Ponceau S, added in glyphosate solution. In droplet sizes range from 149.5 μm to 233.7 μm, deposition of glyphosate on alligator weed leaves treated in the droplet size(VMD) of 157.3 μm was more than that treated in larger droplets. The deposition of glyphosate treated in spray volume of 339 L/hm2 (droplet size 157.3 μm) was 1.54 times of that in spray volume of 694.5 L/hm2 (droplet size 233.7 μm).The deposition of glyphosate was increased slightly when spray volume was higher than 375 L/hm2,and the maximum deposition of glyphosate on alligator weed leaves was about 4.92 μg/cm2 when treated under the concentration of 800 mg/L in droplet size of 149.5 μm. The results indicated that in relative small droplet and low spray volume the deposition of glyphosate on alligator weed would be increased greatly.