The unique optical, electrical, thermal, mechanical properties and outstanding chemical stability of diamond film make it an ideal material for micro-electronics devices in future especially at high temperature, high radiation and corrosion environments. It has been the international interesting subjects that the fabrication of CVD diamond films and their applications. In this thesis, the fabrication of HFCVD diamond films and their applications in photoelectron devices are studied. Firstly, diamond films with different orientation and grain size were achieved by changing the deposition condition in hot filament chemical vapor deposition (HFCVD) system. The UV detectors were fabricated successfully from diamond thin films with different orientation and grain size by the microelectronic processing. Results show that the performance of the detector was related to the grain size of the diamond film. With increasing the grain size, the photocurrent, the ratio of photocurrent to dark current and the net photocurrent increased. In the case of the diamond films with similar grain size, the detector fabricated from (100)-oriented diamond film had a better characteristic of spectral response than the ones from other orientation. In addition, a successive post treatment of the detector in CH4 gas followed by air atmosphere can enhance obviously the spectral responsivity of the UV detector. The orientation, the grain size of the diamond thin film and the post treatment can affect the performance of UV detector significantly. It"s important to achieve the diamond film with big grain size and highly (100)-oriented and use the proper post treatment, which is in favor of fabricating the UV detector with good performance. Secondly, freestanding diamond films were prepared, and ultraviolet photodetectors with ZnO/diamond film structure were fabricated. The surface roughness of nucleation side of freestanding diamond film, the properties of Au contacts on ZnO films and effects of grain sizes on the electrical characteristics of photodetectors were discussed. The results indicated that the surfaces of nucleation sides were very smoother, and the surface roughness of nucleation side reached 1.5nm(1μm×1μm); Due to the bombardment with Au atoms and the annealing process, fine ohmic contacts were formed between Au electrodes and ZnO films; Dark currents and photocurrents of photodetectors were related to the grain size of ZnO films, For the photodetector with a bigger grain size, a lower dark current and a higher photocurrent were obtained; The photocurrent increases swiftly and then saturate gradually with the irradiation time process. Due to using the polycrystalline ZnO films with high densities of grain boundaries which are full of traps, the photoconductor shows the transient UV-response with a long photocurrent rise and decay time of around 10 min and 3 min, respectively. The photocurrent rise and decay process confirmed the carrier trapping effect. Thirdly, the fabrication of NCD films on different conditions for X-ray mask matetrial has been studied. The result shows that the nano-crystalline diamond film has a higher transmission and a smoother surface at deposition temperature of 640℃and gas pressure of 2.5kPa. Hydrogen etching method is applied to the experiments to optimize the parameters. From the charactristic of the structure and optical property, the grain size and surface roughness decrease while the refractive index and optical transmission increase obviously under certain deposit parameters (gas pressure and substrate tempreture) and longer etching time. Optical transmission reaches 51% at the wavelength of 632.8nm. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmission reaches 52.8% at an X-ray photon energy of 258eV, which has meet the requirement for X-ray mask matetrial. The optical performance of the NCD films is mainly co-determined by the two factors of surface roughness and the content of sp~2 phase