The invention discloses a variable-cycle air turbine combined engine of a rocket. The variable-cycle air turbine combined engine of the rocket comprises an axial compressor, a shaft, a main combustion chamber, an air duct, a turbine, an afterburner and an exhaust nozzle, wherein the axial compressor is arranged on the side, with an air inlet, of the main combustion chamber, the turbine is arranged on the side, with an air outlet, of the main combustion chamber, the axial compressor is connected with the turbine through the shaft, the air duct is arranged on the outer side of the main combustion chamber, and is used for communicating the axial compressor with the afterburner, the afterburner is arranged on the exhaust side of the turbine, and the exhaust nozzle is communicated with the afterburner. The variable-cycle air turbine combined engine of the rocket further comprises a fuel gas generator and a second turbine, wherein the fuel gas generator is arranged between the air duct and the main combustion chamber, the second turbine is arranged at the blade tip position of the turbine, and is connected with the axial compressor through the shaft, and an outlet of the fuel gas generator exactly faces the second turbine. The variable-cycle air turbine combined engine of the rocket provides a power system solution scheme for a spacecraft, wherein according to the power system solution scheme, the spacecraft can carry out the long-time economical cruise, and can carry out high-speed maneuver in a short time in a high comprehensive performance mode, and the problem that an existing aviation turbine engine can not carry out self-starting can be solved.