CVD diamond thin films have many unique characters such as high hardness, high elastic modulus, good thermal conductivity and chemical stability, so CVD diamond thin films have wide application on the tools and dies. However, uneven nucleation and low growth rate are two problems which have huge influence on the diamond film deposition and diamond crystals growth. The experimental results indicate that the quality of diamond nucleation and crystals growth depend on the substrate temperature field in the large area hot filament CVD system. Uneven temperature field and improper temperature may result in surface irregularity and also the grain size may become uneven which make the diamond films rough. And the tools with rough diamond film will have serious wear during its application. Therefore the study on substrate temperature field becomes more and more important. This paper simulates the substrate temperature fields during diamond crystal growth and diamond films deposition on tools and dies with finite element software. The influences of deposition parameters of hot filaments in HFCVD system on substrate temperature field are studied. The concrete research contents are as follows: (1). Based on the theory of heat transfer, the equations of temperature field on a large area substrate in HFCVD system is established. And the influences of hot filament parameters such as the radius, spacing and number of filaments, the distance between filament and substrate on the temperature distribution of substrate are analyzed. (2). The substrate temperature fields during diamond crystal growth and diamond films deposition on tools and dies are respectively simulated to analyze the influence of hot filaments parameters on the substrate temperature field. Consequently, the optimum hot filaments parameters of the three depositing processes are obtained from the simulation results. (3). Based on the simulations, diamond coated cutting tools and drawing dies and single crystal diamond are deposited in the HFCVD system by changing the hot filament parameters. (4). Based on the experiments, the surface morphology and quality of diamond films and single crystal diamonds were characterized by SEM after the deposition. And the influences of hot filament parameters on the quality of diamond films and diamond crystals are studied. Meanwhile, the simulation results are validated (5). The diamond growth under the optimum hot filament parameters are studied. The optimum arrangement of seed crystals was established and single crystal diamonds with high efficiency and great crystal shape was obtained, which laid the foundation of developing a new process of depositing large single crystal diamonds. As while, the CVD homoepitaxial coating recovery suggested a new method to improve the grade of crystal shape by HPHT process.