The competition for future resources lies in the deep sea and the key to the development of deep-sea resources depends on the level of deep-sea equipment. To manufacture the equipment served in the deep sea, the key issue is to prepare the metal materials with required properties. High-entropy alloys are gaining increasing attention due to their excellent corrosion resistance in harsh environments, such as the deep sea. It is crucial to reveal the corrosion mechanisms of high-entropy alloys to develop alloys with excellent corrosion resistance and expand the applications of high-entropy alloys. In this review, the corrosion mechanisms and evaluation methods of high-entropy alloys are comprehensively reviewed based on the galvanic corrosion theory, point defect theory, and passivation theory. In addition, the strategies, including alloying and heat treatment, to improve the corrosion resistance of high-entropy alloys are summarized. The aim is to better understand the corrosion behavior of high-entropy alloys and provide theoretical guidance for developing high-entropy alloys with excellent corrosion resistance.