The investigation shows that power semiconductor devices are the most fragile components of power electronic systems. Improving the reliability of power devices is the basis of a reliable power electronic system, and in recent years, many studies have focused on power device reliability. This paper describes the current state of the art in reliability research for power semiconductor devices, mainly includes failure mechanisms, condition monitoring, lifetime evaluation and active thermal control. Among them, condition monitoring technology are classified and summarized by the failure mechanism and the change rules of characteristic quantities; The method of lifetime estimation is illustrated from the practical point of view; Methods of active thermal control are classified and summarized from the two ideas of reducing loss and loss compensation which are refined by the principle of realization. At last, this paper draws the existing problems and challenges of power devices reliability studies.