Metal oxide semiconductors are the most significant materials due to their tunable and wide band gap properties. They are non-hazardous materials. CuxO thin film is a p-type semiconductor material. CuxO has naturel Cu vacancies; it has been predicted by theoretically and by experimentally in different growth technologies. In this paper, Cr element was doped into the CuxO thin film and then microstructural, surface, optical and crystal defects properties effect on band gap structure of the Cr doped CuxO thin film were investigated. Cr doped CuxO thin film was deposited by thermionic vacuum arc thin film deposition. In XRD pattern, CrO2 (110), Cu2O (200), Cu (111), CuO (1 (1) over bar2) and CuO ((2) over bar0 2) crystallite reflections were detected. Cr decorated the Cu vacancies in crystal network. Mean crystal dimension is approximately 15 nm. Deposited thin film is transparent in the visible region. The band gap of the Cr doped CuxO thin film was obtained approximately 2.0 eV. According to the photoluminescence measurement at different excitation energy, some defects were determined. 2.0 eV transition were detected. Finally, deposited thin film is transparent and it has high dielectric constant.