In this work, a PAM(Plasma Assisted Machining) technology was applied to milling of high manganese steel, a typical hard-to-machine materials. For this purpose, a transferred type of arc plasma torch was coupled with a 3-axis milling machine, then, used to heat and soften the surface of a high manganese steel plate in front of a 16 mm end mill with 2 blades and hard coatings. From the test results, it was concluded that the cutting load can be significantly reduced down to 57 % by plasma heating with the power level of 3.9 kW, ensuring the improvement of tool life and surface roughness in milling of high manganese work pieces.