Organic light-emitting device (OLED) has well-recognized advantages in simple structure, low-driving voltage, flexibility, large area and availablity. It shows tremendous commercial applications in optical communication, information display and solid-state lighting, and has been one of the most attractive projects in optoelectronic information field over the last decade. Since 1987, OLED has rapidly developed, its brightness and efficiency has reached the practical demands. However, one of the main challenges to the industrialization is the stability of the device. In this paper, some of the extrinsic and intrinsic degradation mechanisms in OLEDs are summarized and discussed, such as the dark-spot formation, morphological instability of organic thin film, metal-atom diffusion, Alq3 cationic and positive charge accumulation. After that, we summarize the approaches to obtaining the long lifetime OLED. Finally, some perspectives on the stability of OLED are proposed.