High speed machining of the corner of hardened steel mould has a great influence to the entire product performance of the mould. In this paper, with the single factor experiments, the influence of feed per tooth, cutting speed and angle of the corner to the cutting forces, the vibration value and the surface roughness were analyzed. And the cutting parameters were optimized. The cutting forces, vibration value and surface roughness value of the corner of the mould reached the minimum value when the cutting speed was 80 m/min and the feed per tooth was 0.006 mm/z in the experiment. The surface quality of corner with angle of 90o was better than the corner with angle of 60o and 120o with various milling parameters.