The invention discloses a method for measuring optimum extraction condition of a metal extractant, which comprises the following steps: preparing a micro-dispersed liquid drop emulsion by the metal extractant through a liquid-liquid micro-dispersion method; measuring the surface potential of the micro-dispersed liquid drop emulsion, and determining the optimum extraction condition according to the surface potential. A method for determining the optimum extraction condition comprises the following steps: S1, a group of experiments are performed, in the group of experiments, one specific extraction parameter in several extraction parameters is changed in each experiment, other extraction parameters are unchanged, and surface potential of each experiment is measured; S2, the surface potential values measured in each experiment in the group of experiments are compared, the lowest absolute value of the surface potential values in the experiment is taken for corresponding to the value of the specific extraction parameter, so that the optimum extraction condition is determined; and S3, the above steps are repeatedly carried out, and the optimum extraction condition can be respectively determined when the other extraction parameters are changed. The method provided in the invention is accurate and effective, and the problems of measuring range restriction and long preparation time while determining the optimum extraction efficiency condition in a traditional mode can be avoided.