This paper investigates the unsteady flow characteristics within the inlet during the ram-to-turbo transition of a Turbine-Based Combined Cycle （TBCC） engine. Through a combined approach of wind tunnel test and Computational Fluid Dynamics （CFD） simulations， it analyzes the evolution of the inlet shock system and the static pressure variation patterns along critical flow path locations， and acquires the dynamic restart characteristics of the low-speed duct during inlet mode transition and the influence of flow splitter rotational speed on this process. The results indicate that during the progressive opening of the low-speed duct under turbine-mode startup conditions， six distinct phases occur： in phase 1， flow splitter deployment initiates boundary layer ingestion into the duct， causing minor static pressure drop； in phase 2， supersonic core flow enters the duct， triggering significant static pressure rise； in phase 3， flow accumulation induces pressure buildup and shock train forward propagation， followed by shock traversal past the bleed cavity， with subsequent cavity depressurization causing shock recession； in phase 4， cyclic expansion/contraction of the low-speed duct separation bubble induces shock oscillation； in phase 5， shock expulsion along the separation bubble triggers inlet buzz； in phase 6， reduction in downstream Throttling Ratio （TR） terminates buzz， enabling low-speed duct restart. During the low-speed duct restart process， the rotational speed of the flow splitter vanes influences both the frequency and amplitude of pressure oscillations within the flow path， with lower rotational speeds resulting in reduced oscillation frequencies and increased amplitudes. Moreover， during low-speed duct restart， the rotational speed also affects the onset timing of buzz， where lower speeds more readily trigger inlet buzz in the low-speed duct. This study provides a theoretical foundation for achieving smooth mode transition in combined-cycle engines.