Abstract: The CuO-ZnO heterojunction gas sensor is a new type gas sensor, and it has many advantages, such as low cost, simple processing, and convenient testing etc. In this work, the sensitive property of the sensors to gases was studied the under different ratios of ZnO to CuO. The resistance-temperature properties of samples were tested, and their sensitivities for different temperature and gases were also measured. The testing results and their sensing mechanisms are analysed and discussed in this paper.