A new testing research on an existing engine provides an efficient way to explore critical engine technology.A new method is proposed to develop VCE (variable cycle engine) from a conventional gas turbine (turbofan) engine.This paper also presents a configuration promotion project with introduction of selector valve,and puts forward VABI (variable area bypass injector) and rear VABI.The first stage of high pressure compressor is changed to a CDFS (core-driven fan stage).The working principle of the VCE is stated.Based on the components′ performance level of conventional turbofan engine,a primary overall performance project is carried out and a numerical simulation on VCE is conducted.The calculation results show that the thrust can be increased by 5% to 8% in supersonic cruise using single bypass mode.Although specific fuel consumption (SFC) cannot be decreased obviously in subsonic cruise using double bypass mode,the engine inlet air flux can be increased by 5%,so the spillover is reduced and installed performance of the engine can be improved.