Abstract: This study provides the first systematic clarification of the theoretical foundations and mechanistic structure of the sequential training model composed of Conjugate Sequence System (CSS) and Block Periodization (BP), as well as their ontological differences and complementary relationships at the mesocycle level. Based on this analysis, an operational integration strategy for high-performance athletes is proposed. Using a literature review and mechanistic analysis, the conceptual genealogy, key modules, and structural relationships of these two models were systematically examined, and their typical application pathways were synthesized in relation to sport-specific characteristics and competition-calendar complexity. The results indicate that CSS is grounded in the Long-Term Delayed Training Effect (LDTE) and the conjugate sequencing of abilities and training loads. By concentrating loads on clearly identified performance bottlenecks and facilitating delayed transfer, CSS promotes substantial adaptive shifts within a mesocycle. In contrast, BP is organized around the Residual Training Effect (RTE) and employs the "accumulation–transmutation–realization" structure to combine a limited number of abilities in a sequential manner, thereby enhancing temporal training efficiency and load–recovery alignment during multi-peak competitive seasons. Conceptually, the two models address distinct temporal dimensions of training adaptation: CSS emphasizes when peak performance emerges, whereas BP emphasizes how long training effects can be retained. Their integration may thus form a complementary paradigm in which BP establishes the structural framework and rhythm of mesocycle organization, while CSS is embedded within critical adaptive windows to deliver targeted capacity breakthroughs. The findings suggest that CSS and BP represent two mechanistic extensions of classical periodization at the mesocycle level. In practice, the more complex the competition calendar, the more appropriate it is to employ BP to regulate structural organization and timing of peak performance; conversely, the clearer the limiting performance bottleneck, the more suitable CSS becomes for targeted breakthroughs through concentrated loading. Their coordinated application can enhance both the scientific basis and practical operability of high-performance training periodization, hence providing a new theoretical framework and methodological pathway for the further development of periodization theory and elite training practice in China.