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The important operating characteristics of pulsed Pressure Gain Combustion (PGC) propulsion are the pressure gain of the combustor component and the propulsive performance gain of the engine. A ramjet-type valve/valveless air-breathing pulsed detonation engine with a super-sonic internal compression inlet is investigated. Based on an ideal thermal cycle, the ideal equivalent pressure ratios (πcb) of the Pulsed Detonation Combustor (PDC) are obtained theoretically which are directly related with the propulsive performance of the engine. By introducing an orifice loss model into the cycles, the critical pressure drop ratios through the orifice for the PDC achieving pressure gain and the engine achieving thrust gain are studied. More influencing factors are inves-tigated by the use of a one-dimensional (1-D) numerical simulation model. The operating charac-teristics of the pulse detonation engine are investigated with changes of the valve type, the inlet/outlet area ratio of the PDC, the nozzle area ratio, and flight conditions. All these factors can affectπcb of the PDC, andπcb can be optimized by changing the geometry of the engine. The most impor-tant influence parameter is the valve type. When using an orifice-type aerodynamic valve, simula-tion results show that the PDC cannot achieve the pressure gain characteristics. When a supersonic internal compression inlet is introduced to the engine, whether the Pulse Detonation Engine (PDE) can achieve thrust gain comparable with that of an ideal Brayton cycle engine not only is related to the pressure gain of the combustor, but also needs to optimize the engine structure to reduce the total pressure loss.