Abstract: To investigate the impact of shuttle performance and layer-switching strategies on the efficiency of the Tier-to-Tier Automated Vehicle Storage and Retrieval System (TTAVS/RS), a parameterized and modular efficiency evaluation model for AVS/RS was developed based on the discrete event simulation method. Employing the control variable approach, the model analyzed the effects of shuttle quantity, shuttle speed, and rack layout on system efficiency, while examining the influence of four layer-switching strategies. Simulation experiments with incrementally increasing shuttle quantities revealed that the goods lift constitutes the primary bottleneck constraining system efficiency, and excessive shuttles reduce per-shuttle utilization; compared to the Tier-Captive mode, the Tier-to-Tier mode more effectively balances the handling capacity between shuttles and lifts, thereby enhancing shuttle utilization. Comparative experiments on layer-switching strategies demonstrated that, relative to the commonly adopted “first-come-first-served” strategy in engineering, the “shortest origin distance first” strategy yields superior performance, improving system efficiency by 3.1%–5.8%.