The invention relates to an oil supply device and method for frequency conversion and speed control of a fuel pump for a fuel machine, and belongs to the technical field of the fuel machine. The oil supply device comprises a fuel machine control system, a frequency converter, a variable frequency motor, a fuel oil supplying pump and a rotating speed sensor; the frequency converter is connected with the variable frequency motor, the fuel machine control system is connected to the frequency converter, the fuel oil supplying pump is connected with a gas turbine through a fuel adjusting system, and a bypass opening of the fuel adjusting system is connected with an inlet of the fuel pump; and the rotating speed sensor is installed on the gas turbine, a signal line of the rotating speed sensor is connected with the fuel machine control system, and the fuel machine control system controls the rotating speed and the flow of the fuel pump according to the rotating speed to form closed-loop control. By means of the oil supply device and method, the rotating speed of the motor is changed by changing the power frequency of the motor, the oil pump capacity, starting and low-state less oil supplying of the oil pump are changed along with changes of the state of the fuel machine, and therefore the aim of energy saving is achieved. Soft start of the oil pump is achieved, and the service life of the motor and the pump is guaranteed. As the oil returning amount is greatly reduced, the stability and the adjusting accuracy of the adjusting system can be improved.