In this study, wire electrical discharge machining (WEDM) was implemented to process polycrystalline silicon ingot, and the influences on processing characteristics were examined. There are two different dielectrics, pure water and pure water with sodium pyrophosphate powder, that were experimented to compare their effects on cutting speed: kerf loss and surface roughness. In the experiment, sodium pyrophosphate powder has shown that it has enhanced process efficiency and has improved surface smoothness. From the results, it has been found that by using phosphorous dielectric, the cutting speed increased 2.4 times than pure water. Meanwhile, by using phosphorous dielectric, it caused high temperature and brought about the electrolysis effect, which improved its surface roughness enhanced 16% compared with pure water. This also decreased kerf loss and boosted up the material utilized. Through WEDM, high-temperature characteristic forces the phosphorous element of the dielectric to infiltrate on the cutting surface of the polycrystalline silicon ingot. The result proved that using phosphorous dielectric on WEDM could increase the efficiency and surface roughness, and could infiltrate phosphorous element on the surface of the polycrystalline silicon ingot. These findings could be future references on the researches of solar cell in both industrial and academic fields.