To address the wide-speed-range intake requirements of turbine-based combined cycle (TBCC) engines, this study proposes an axisymmetric dual-flowpath variable geometry TBCC inlet scheme with three adjustable components: (1) fore-aft translation of the inlet lip for capture flow regulation, (2) fore-aft translation of the flow splitter for flow distribution control during mode transition, and (3) fore-aft translation of the ramjet cowl for contraction ratio adjustment to ensure stable ramjet operation across the speed range. Numerical simulations were conducted to analyze the aerodynamic performance and flow characteristics under various backpressure conditions at typical operating states, including turbojet mode, ramjet mode, and transition phase. The results demonstrate that the pro-posed inlet configuration maintains stable operation across the Mach number range of 0–6.0. In ramjet mode, the total pressure recovery coefficient and exit Mach number decrease with increasing backpressure. In turbojet mode, elevated backpressure weakens the shock waves within the duct, leading to improved total pressure recovery. During mode transition, the ramjet channel exhibits enhanced backpressure tolerance, while the turbojet channel shows slightly reduced resistance to backpressure. Excessive backpressure causes shock wave advancement to the splitter plate, inducing flow deflection, while specific backpressure levels trigger flow field oscillations. This study elucidates the relationship between backpressure and the performance characteristics of an axisymmetric dual-flowpath variable geometry TBCC inlet, providing valuable insights for future research in this field.