With the development of both a simplified model for calculating the mode transition performance of the dual-flowpath combined inlet and the simulation model for high-Mach turbine engine under the windmilling condition,the dynamic performance simulation of full transition process from turbo mode to ram mode for a Mach 7 over-under Turbine-Based Combined-Cycle (TBCC) engine was conducted. Mode transition was divided into four typical sub-processes,including ramjet cool open,afterburner staged shutdown,turbine engine throttle down, and turbine engine cool down (windmilling close). A mode transition strategy was proposed based on the principle of smooth thrust variation. The simulation results show that: TBCC engine thrust transition mainly occurs in the sub-process from full augmentor to non-augmentor during mode transition; both the ramjet operating in the cool open condition and the turbine engine operating in the windmilling condition will deliver negative thrust,the maximum value of which will account for 5.3% and 13.7% of the total thrust after mode transition,respectively,during the early and later period of mode transition; when the turbine engine gets into the windmilling operation,mode transition work points are located at the low-speed and high-flow region of fan and compressor characteristics map,and the pressure ratio of fan and compressor varies to 1.0 along with the decrease of air mass flow,which is in good agreement with relevant experimental results. 2018, Editorial Department of Journal of Propulsion Technology. All right reserved.