Relay protection devices are the first line of defense in power systems, and their reliability is crucial. Temperature is the primary factor that leads to the failure of relay protection devices, significantly affecting their reliability. However, current reliability impact analyses of relay protection devices, particularly their failure rate prediction, rarely consider the influence of temperature. In view of the above problems, the influence characteristics of temperature on relay protection devices are analyzed in detail, and a failure rate prediction method considering temperature is presented. First, the architecture of typical protection devices is introduced. The heat transfer forms and temperature characteristics in different installation environments are analyzed, and the temperature distribution characteristics of the device are studied. Next, reliability physics is used to quantitatively analyze the temperature influence characteristics of device failure. Combined with the device architecture, a failure rate prediction method for a relay protection device considering temperature is then proposed. Finally, from the measured temperature and failure rate prediction results in different environmental conditions, the rationality of the proposed method is verified by combining with the engineering data and experience.