The thymus is a key organ for T-cell development and the establishment of central immune tolerance. Research on immune function changes and long-term health risks following thymectomy is characterized by significant population heterogeneity and controversial conclusions. This article systematically reviews the key immunological alterations after thymectomy - including reduced T-cell receptor (TCR) repertoire diversity, regulatory T cell (Treg) dysfunction, accelerated immune aging, and compensatory immune responses, and clarifies population differences in postoperative risks of infection, autoimmune diseases, and tumors, as well as the impact of surgical approaches. The clinical outcome after thymectomy is not solely determined by thymus loss, but rather depends on a dynamic balance between "immune deficiency risk" and "host compensatory capacity," which is modulated by multiple factors such as age at surgery, extent of resection, and individual immune status. This review proposes a "risk-compensation balance model" framework, providing an integrated theoretical basis for explaining the heterogeneity in outcomes across different populations and surgical methods. It also holds significant implications for future efforts in individualized surgical decision-making, establishment of stratified immune monitoring systems, and exploration of targeted immune intervention strategies.