Electrical Discharge Machining (EDM). It is able of machining structure of very complex geometry, hard material components,that are precise and difficult-to-machine such as,composites,ceramics, carbides,hard metal etc.widely used in die and mold making industries,aerospace,railways,aeronautics and nuclear industries. AISI P20 Plastic mould steel that is generally supplied in a hardened and tempered condition. good machinability, better polishability,These steel are categorized as difficult to machine materials,have greater strength and toughness are usually known to create major challenges during conventional as well as non-conventional machining.The E.D.M process is finding out the consequence of machining parameter such as tool diameter,discharge current and pulse on time on the material of work piece. Using U-shaped cu tool with internal flushing. A well-designed experimental scheme was used to reduce the total no.of experiments.Parts of the experiment were conducted with the L18 orthogonal array based on the Taguchi method.observed values of Responses of Material Removal Rate(MRR), Tool Wear Rate(TWR) and over cut(OC).