Abstract: In order to obtain the mechanism of partial discharge on contaminated insulation surface adhered with metal conductor, artificial contamination test of small size composite insulating material specimens attached with metal conductors was carried out. Combining with simulation analysis, the difference in the discharge phenomena caused by the relative size between width of contamination layer and adhered metal was studied in depth, which can provide a theoretical basis for proposing practical measures to suppress partial arcs. Test and simulation results show that dry band is the most essential factor affecting partial arc discharge. The location of the dry band and the location of the partial arc are determined by the suspended potential conductors. The relative size of fouling layer and attached conductor has obvious influence on partial discharge. When the width of the fouling layer is much larger than the size of the attached metal, the dry band can’t penetrate the fouling layer. The maximum electric field strength of the dry band can’t reach the initial electric field strength of the discharge, and there will always be no obvious partial arc near the metal. When the width of the fouling layer is about the same as the size of the attached metal,the dry band will penetrate the fouling layer and bear most of the voltage, so that the electric field strength exceeds the initial discharge field strength, and there will be obvious partial arc near the metal.