The invention discloses a chemical compound cycle gas turbine device with a wide power range and a control method. The chemical compound cycle gas turbine device comprises a gas compressor, a fuel cell, a combustion chamber, a hydrogen source, turbines and an electric generator. The first output end of the gas compressor is connected with the cathode input end of the fuel cell, and the second output end of the gas compressor is connected with the first input end of the combustion chamber. The anode input end of the fuel cell is connected with the hydrogen source, and the cathode output end ofthe fuel cell is connected with the first input end of the charging turbine. The anode output end of the fuel cell is connected with the second input end of the combustion chamber. The third input endof the combustion chamber is connected with the hydrogen source. The output end of the combustion chamber is connected with the second input end of the charging turbine. The output end of the charging turbine is connected with the input end of the power turbine. The output end of the power turbine is connected with the electric generator. A first valve and a second valve are arranged on a pipeline through which the gas compressor communicates with the combustion chamber and a pipeline through which the gas compressor communicates with the fuel cell correspondingly. According to the gas turbine device and the control method, the structure is simple, the power range is wide, the design is reasonable, tail gas is fully used, and waste is avoided.