Graphite electrode have many advantages such as quicker EDM speed, better machining accuracy, higher heat resistance, lower electrode wear in EDM(Electric Discharge Machining). It can meet the processing requirements of complex surface, stiffener, air-cooled fin and fine mesh structure in the fields of automobile, home appliances, communication, electronic industry, etc. High speed milling is one of the major process methods to manufacture precise graphite electrode with complex shape. Many enterprises try to use diamond tool for high speed milling of graphite electrode due to the severe wear of carbide tool. However, because of lack of further research on the lifetime of diamond coated tool when high speed milling of graphite, tool wear mechanism and optimization of high speed milling technology, there are many problems in its application. The advantages of diamond coated tools and high speed milling cant not exert. Focusing on the characteristics of graphite electrode, this paper uses diamond coated tools to processing graphite instead of carbide tools. This paper mainly research on the lifetime of high speed milling graphite with diamond coated tools, the effects of cutting speed, feed rate per tooth, radial depth of cut, axial depth of cut, and material of tools on the cutting forces. Optimal selected the process parameters based on the orthogonal experiment of cutting force. This paper has eventually studied the surface quality of graphite electrode by high speed milling with diamond coated tools and comparison with TiAlN coated and WC tools. The main conclusion of this paper are: The lifetime experiment of diamond coated tools high speed milling graphite shows that: (1)The surface of diamond coated tools is not fully homogeneous, there are big particles of diamond gather into cluster on the surface. (2) After cutting 100m, any wear on the tools surface can not be found and the cutting force changed little. When 350m, failure occurs on the cutting tools and the cutting force increases in a sudden. (3)The order of the lifetime of cutting tools on the same cutting conditions but different tools materials is: Diamond>TiAlN>WC . The experimental result of the influence of cutting factor on cutting force experiment display: (1) Negative cutting force appear during real-time cutting, and cutting force has great fluctuation. (2) Cutting force follow the cutting the speed first increase and then decrease. The max cutting force appear when the cutting speed increase to 240m/min. When feed per rate tooth increases, the component force of cutting force increases slowly, the amplitude of fluctuation tends to first increase and then decrease. When radial depth of cut increases, cutting force is almost invariant, but fluctuation of cutting force is significant. Cutting force first increase and then decrease when axial depth of cut increases, when depth 9mm reach the optimal. (3) The cutting force of down milling is smaller then up milling, down milling is recommended. (4)Cutting forces of different materials of cutting tools is: WC >Diamond> TiAlN (5) The optimal combination of process parameters that makes the minimum cutting force is, cutting force 360m/min,feed per tooth 0.15mm/z, radial depth of cut 0.9mm, axial depth of 9mm. The research of diamond coated tools wear mechanism has found: (1) The tools wear and failure mainly distribute on basic knife. (2)The main wear form of tools is adhesion wear and abrasive wear. The main failure forms are coating shedding and tipping. (3) Mechanical impact and the shedding of graphite dust are the main reason that leads to the failure of diamond coated tools. Research on the surface quality of graphite has obtained: (1) Bigger material removal rate can be got by the diamond coated tools. (2) The 3D profile of the surface of high speed milling graphite electrode displays very unevenness. (3) The surface quality of graphite milled by diamond coated tools is worse than of TiAlN coated tools, The surface quality of graphite down milling is better than that of up milling.