The invention discloses a design method of a three-power combined engine with coexisting of supersonic 
combustion combustor and a subsonic 
combustion combustor, and relates to a combined engine. According to the flight mission, the overall 
performance requirement is formulated, a basic flow field is designed based on the overall 
performance requirement, and then a three-dimensional internal turning air passage is obtained by streamline tracing. In a three-dimensional internal turning air passage outlet, according to the overall performance of the engine, the inlet and outlet parameters of thesupersonic 
combustion combustor are obtained, and the supersonic combustion combustor is designed. In front of a supersonic combustion combustor inlet, an ejection 
rocket passage of corresponding sizes are arranged based on a thrust requirement of the Ma2-5 engine, and a central cone, a 
rocket engine and the subsonic combustion combustor are included. According to the flow requirement of the engine in a Ma0-2 stage, the area of a 
turbine passage inlet is calculated by using the flow formula shown in the specification, an opening is formed in the wall surface of the three-dimensional internal turning air passage, and the 
turbine passage is arranged. A common 
tail spraying 
pipe with an adjustable geometric area is arranged at a supersonic combustion combustor outlet and the 
turbine passage outlet, and a spreader plate is designed according to the different working conditions of the 
tail spraying 
pipe.