High Speed Milling (HSM) is well known as an innovative key technology for modern machining. HSM can obtain very high surface qualities, subsequent manually finishing operations can be eliminated in many cases totally or at least partially. Theoretical and experimental researches have proven that the cutting force in a high speed milling process has significant influences both on surface roughness and deflection of the cutting tool. In this paper, mould steel for high speed milling experiments by multi-factor test on the high speed milling machine tools. By studying the relation of overhang length, cutting speed and cutting force of cutting parameters, the cutting force tested is analyzed in high speed milling. When mold steel is cut at high speed, the influence of cutting speed on cutting force is studied, which has a guidance in the actual production.