Organic light-emitting devices (OLEDs) have attracted wide attention in the display industry owing to their excellent characteristics, such as active luminescence, fast response time, wide viewing angle, and compatibility with flexible electronics. Nevertheless, organic luminescent materials are vulnerable to environmental moisture and oxygen, and they fail once they come in contact with water and oxygen. The formation of black spots is one of the main factors affecting the product yields of these devices. Relevant studies have proposed several mechanisms for the formation of black spots; however, there is no specific model. In addition, current models of the formation of black spots are relatively vague and unpredictable. To reduce and prevent the formation of black spots, this study summarizes the causes of black spot formation, discusses the formation mechanism of black spots, and provides preventive measures.