Study on the synthesis and properties of CVD diamond film for its applications in devices has been presented in this thesis.CVD diamond film is one of the material research focuses in 1980s. It has a lot of distinguished properties such as high hardness, large Young" s modulus, very low coefficient of friction, good thermal conductivity, wide band gap, high mobility of electrons and holes, negative electron affinity, high radiation tolerance, chemical inertia, innocuity, and so on. These advantages, therefore, make it idea candidates for many applications including the optical windows, the coatings of cutting tools and magnetic disks, the heat exchange material (heat sink and heat spreader), excellent semiconductor material to be used under high speed, high temperature or high power, the cold cathode field emission flat panel displays, etc.Various techniques, including hot filament-assisted CVD (HFCVD), microwave plasma-assisted CVD (MPCVD), radio frequency plasma-assisted CVD (RF-PCVD), direct current plasma-assisted CVD (DC-PCVD), electron cyclotron resonance microwave plasma-assisted CVD (ECR-MP-CVD) and combustion flame-assisted CVD, have been employed to deposited CVD diamond films. Since the deposited diamond films have high quality and the apparatus is relatively cheap, HFCVD and MPCVD are often adopted for the fabrication of applied diamond films. Compared with MPCVD, HFCVD is more suitable for the large area diamond film synthesis. Using this method, the film diameter has been fabricated up to 30 cm.The deposition of diamond films with high quality depends on the good comprehension of the film formation mechanism and the adoption of the optimized deposition parameters. Therefore, in-situ laser reflectivity measurement was used to study on the diamond film growth and properties in real time. The research results were adopted for the optimized growth conditions of diamond films with high quality.