Variable cycle turbofan-ramjet (VCTR) engine is a promising propulsion system candidate for future Mach 4+ vehicles. Compared with conventional turbine engines, the VCTR engine has a higher thrust-to-weight ratio, a smaller diameter and a more compact structure. A component-based simulation model is developed to explore the operating characteristics of a high-speed VCTR concept. Modeling methods of variable-geometry components are characterized in this paper, and then, the way to build the VCTR model solver is described. The VCTR engine simulation model is validated by the numerical and experimental results of double bypass (DB) variable cycle engines from NASA technical reports. Performance and control law of the VCTR engine along the flight trajectory with flight Mach number varying from 0.5 to 4.0 are obtained to maximize net thrust and compared with that of a conventional two-spool afterburning mixed-flow turbofan (MFTF). Results show that the VCTR's performance is highly dependent on the fan characteristics and limited by various operating constraints, such as fan surge margin, turbine inlet temperature, and compressor discharge temperature. In addition, the thrust level of the MFTF with the variable-area low-pressure turbine is close to the VCTR engine.