Diamond coated cutting tools are prepared by depositing a diamond thin film on cemented carbide substrate with Chemical Vapor Deposition (CVD) method. Diamond coated cutting tools have unique combination of excellent physical properties, such as high hardness and toughness, good thermal conductivity, outstanding wear and chemical resistance and low friction coefficient, and have wide application potential in the machining of aluminum alloys with high silicon-content, metal matrix composite material, engineering ceramics, non-ferrous metals, and fiber reinforced plastics. The coating technology is relatively simple and cheap, and can be applied to cutting tools with complex shape, such as milling cutters, twist drills and taps etc., by depositing the diamond film on the substrate material directly, so that they can be employed to machine difficult-to-cut materials with high efficiency. The thesis aims at some key technological issues regarding on the deposition process of diamond coated cutting tools with complex shape and their application in machining, such as increasing the nucleation density in the beginning of diamond coating, improve the adhesive strength between the diamond film and the substrate, and the cutting performance evaluation. The main research contents of the thesis are as following: 1. The non-equilibrium thermodynamics and the dynamics model of the diamond thin film deposition was studied; the temperature field distribution on the substrate in the reaction apparatus was computed; the role of the temperature field distribution and relevant factors in diamond film deposition quality and speed is analyzed; and the deposition process is optimized based on the inspect results and data of the diamond deposition experiments conducted in the lab. 2. Pretreatment methods suitable for cemented carbide substrate with complex shape are investigated.