To develop a propagation model of a local discharge on a wet polluted insulator, the authors have examined an electric field near a tip of the local discharge on an electrolytic solution simulating the wet polluted insulator surface. The local discharge was propagated on the solution under the impulse voltage. The local discharge is considered to propagate by ionization in the air near the tip of the local discharge. Therefore, to calculate the propagation of the local discharge, the electric field distribution near the tip of the local discharge must be previously known. In this paper, the authors measured the electric potential on the solution near the tip of the local discharge. Furthermore, the potential was obtained by calculation with the image method. It was found that the calculated values agree well with the measured values.