Against the backdrop of building a unified national electricity market and integrating high shares of renewable energy, China is forming a multi-level, cross-regional market structure. Transactions concluded at different levels, regions, and time points ultimately act on the same interconnected grid during real-time delivery, making the efficient and accurate calculation of available transfer capability (ATC) and the design of its allocation mechanisms critical. This paper first clarifies the concept and theoretical framework of ATC, and summarizes the main technical approaches and limitations of existing calculation methods. It then reviews research progress in typical markets that simultaneously address ATC calculation and allocation, highlighting their characteristics and shortcomings. Building on this, the paper compares ATC calculation and allocation mechanisms in PJM, Europe, and the China State Grid and China Southern Grid regions, revealing the institutional logic and market suitability underlying different designs. Finally, it outlines future research and practical development directions and proposes optimization recommendations for ATC calculation and allocation mechanisms in light of China’s market development needs.