Abstract: Diamond films were deposited on GaAs by Microwave Plasma enhanced Chemical Vapor Deposition（MPCVD） method. The quality of the deposited films were optimized by polishing, surface oxidation and annealing firstly, then Au and Al electrodes were deposited on the surface by the radio frequency and magnetron sputtering method, and simple diamond film radiation detectors were prepared finally. SEM and Raman spectra were used to investigate the quality of deposited diamond films, results showed that the films were 100 oriented, smooth and high- quality. The property of the prepared detectors was characterized by the photo- current and dark- current of the radiation detectors when radiated by 5.9 keV⁵⁵ Fe X-ray.