Abstract: Micro weighing method was used to determine the point of run off ( POR ) of spray liquid and the maximum retention ability ( Rm) on plant leaves concerned. Both immersion method and spray method were used to study the Rm on plant leaves. Based on Young's equation, relationship Rm and adhesion force was revealed by immersion method. Relationship between Rm and adhesion work, γ ×(COS θ +1) was also revealed by spray method. The Rm could be increased on difficult to wet leaves, like rice, if surfactants were added, but decreased on easy to wet leaves too, like cotton.