Abstract: The total characteristics of a Supersonic Through Flow (STF) fan propulsion system of unconventional configuration have been studied.Therefrom some conclusions are obtained as:1.The system's bypass ratio must be actively controlled by adjusting both core and bypass engine's through flow areas.2.A general propulsion system with a bypass ratio variable cycle is able to hold a higher fan compression ratio or a stronger fan power in supersonic flight,when it is coupled with a variable core nozzle critical section area.3.For this new concept propulsion system,the specific thrust per unit of the total air mass flow does not vary with altitude up to the stratosphere.Some calculational results are presented briefly to support the above mentioned conclusions.