Overhead transmission line insulators are designed to perform dual functions namely electrical protection and mechanical support. However, irregular distribution of voltage and electric-field in the insulators may lead to corona, partial discharge, premature aging and indeed flashover. An attempt has been made with finite element software to calculate the voltage and electric-field distribution in this paper. QuickField™ Professional software is adopted to simulate the distribution of
voltage and electric-field along the insulator surface with and without the presence of contaminants. Glass insulator, particularly cap and pin insulator is taken as main research object. The result shows that the contaminated insulator distorts the distribution of voltage and electric-field significantly. Therefore, vital to study both voltage and electric field distribution as it is valuable for designing insulator as well as to predict the performance of the insulator under contaminated conditions..