Abstract: Power electronic devices are the core components of modern high power converters. With the increase of the power levels, the requirements of the reliability become more and more critical. There are still lack of efficient evaluation methods of reliability, especially for the applications which require high power and volume density. The traditional design methods can no longer satisfy the requirements. Therefore, in order to improve the power and volume density of the devices, the accurate characterizations of the working mechanism and reliability margin are of great need. Firstly, this paper analyzed the failure mechanisms of the devices and concluded the current research situations of power electronic devices combing the research results of the authors’ project groups. Then, the failure mechanisms of power devices are analyzed from perspectives of outer and inner affects. Finally, from the perspective of overvoltage, overcurrent and fatigue failure, quantitative evaluation methods are proposed to evaluate the device failures, especially focusing on the physical methods, and verified the effectiveness by taking diodes and insulated gate bipolar transistors as examples. This paper gives supports to the extreme applications of power electronic devices.