Abstract: The fatigue failure of coiled tubing is a critical factor restricting the development of equipment and technology. In particular, the complex operating environments and severe service loads encountered in deep and long-horizontal-section oil and gas development impose higher demands on its fatigue performance. To promote the safe application and advancement of coiled tubing technology, this paper systematically reviews the research history of coiled tubing fatigue, analyzes existing research achievements, and identifies key technical challenges that need to be addressed in the future. The origins of coiled tubing fatigue research are traced, representative findings in this field are comprehensively summarized based on literature statistics, and the shortcomings of current research methods and evaluation systems for coiled tubing fatigue are systematically reviewed. The study indicates that existing approaches have certain limitations, including the difficulty of effectively integrating real-time engineering service data, insufficient consideration of high-cycle fatigue damage, and inadequate adaptability to the complex and variable downhole conditions in deep wells. In view of these deficiencies, it is suggested that future research should focus on the following aspects: first, revealing the fatigue failure mechanisms of coiled tubing at cross-scale micro and meso levels; second, developing data-driven methods for real-time prediction of coiled tubing fatigue life; and third, constructing an engineering early-warning system based on digital twin technology. This review is expected to provide scientific reference and guidance for the innovation and application of coiled tubing technology.