By using the plasma CVD method with hydrocarbon and carbon monoxide gas mixtures with hydrogen，a synthesized diamond film was deposited on cutting tools. In order to clarify the wear characteristics and cutting perfomance of the diamond coated tools，turning tests were carried out on Al-Si alloy，carbon fibre reinforced polymer（CFRP）,glass fibre reinforced polymer（GFRP），and titanium alloy. The diamond coated tools were found to have a cutting performance equal to that of sintered diamond tools when machining materials which did not present the grearest cutting difficulties such as low Si Al alloys，GFRP and CFRP. However，when machining high Si Al alloys，the synthesized diamond film showed a cutting performance inferior to that of sintered diamond tools.