A gas turbine system comprises a gas turbine, a fuel system, a control system and a start motor used for starting the gas turbine. The fuel system is connected with a combustion chamber to supply fuelto the combustion chamber. The control system comprises a motor control loop, and the gas turbine system controls the start motor through the motor control loop. The motor control loop comprises a motor drive circuit, and the motor drive circuit controls the operation of the start motor when the start motor operates in an electric motor mode. The gas turbine system can be started smoothly and safety and runs stably. The invention further discloses an operation method of the gas turbine.