In this study, nickel oxide (NiOx) thin films were prepared by direct current (DC) reactive magnetron sputtering. The various properties of NiOx thin films including deposition rate, morphology, electrical and optical properties as well as grain structure and chemical composition were systematically investigated. The material properties of NiOx were finely modified under the monitoring of target voltage during sputtering. NiOx thin films were applied as hole transport layers (HTLs) in all-inorganic CsPbI2Br perovskite solar cells (PSCs). The highest efficiency of 12.6% had been achieved for the optimized all-inorganic CsPbI2Br PSCs with the inverted structure of Glass/FTO/NiOx(HTL)/CsPbI2Br/ZnO@C-60 (electron transport layer, ETL)/Ag. The PSC still yielded over 90% of its initial power output after 10 h operation without encapsulation.