Abstract: Diamond is a very attractive material to realize radiation detectors due to its exceptional electrical and optical properties, but the detector performances intensively depend on the film quality. In present work, (100) oriented CVD diamond films with different quality obtained by a hot-filament chemical vapor deposition (HFCVD) technique were used to fabricate radiation detectors. 5.9 keV X-ray from a 55Fe source was used to measure the photocurrents and the pulse height distributions (PHDs) of CVD diamond detectors. For the detector with a better film quality, the dark-current of 16.3 nA and the photocurrent of 16.8 nA were obtained at an electrical field of 50 kV/cm. The time-dependent photocurrents performed in the darkness indicate that the photocurrents initially increase and then level off. The peak of the pulse-height discrimination is well separated from the noise, indicating a higher counting efficiency and a higher signal-noise ratio.