Amorphous selenium alloy (a Se alloy) is currently of great interest as X ray imaging receptor due to its high resolution. The a Se alloy films are deposited by vacuum evaporation, the transport properties of hole and electron are measured by time of flight technique. Some factors, which affect the properties of a Se alloy film, are discussed. X ray photocurrent is measured by using 400μm thick film. The results show that linear photoelectric conversion existed in a Se alloy film, and its sensitivity to X ray irradiation depends on electric field. The calculation indicates that about 45 eV is needed for X ray to release an electric hole pair in a Se alloy film at 10 V/μm electric field.