In this study, a Ti-diamond-Ti structured ultraviolet photodetector was fabricated on a homoepitaxial diamond layer with an oxygen-terminated surface. The properties of the Ti/diamond schottky contact were measured using X-ray photoelectron spectroscopy, and the barrier height was found to be 1.15 eV. At a bias of 3 V, the responsivity at 210 nm was only 4.29 mA/W, while at 12 V, the responsivity increased rapidly to 51 mA/W. The increase can be ascribed to the photocurrent gain. With the further increase in voltage, an avalanche effect was produced, and the responsivity could reach 1.18 A/W at 50 V. Moreover, the transient response behavior of the photodetector exhibited a good repeatability and response speed.