The present invention discloses a method and a system pertaining to the field of oil production engineering. According to the method, the crank complete-cycle operation uses a utility frequency driving mode, and the crank incomplete-cycle pumping operation and the crank incomplete-cycle no-pumping, operation use a variable, frequency driving mode. The system is provided with a utility frequency loop and a variable frequency loop which are provided with a common input terminal and a common output terminal. The common input terminal of the utility frequency loop and the variable frequency loop is connected to a utility frequency power supply circuit, and the output terminal is connected to a driving electric machine of the oil pumping unit. A frequency changer is configured in the variable frequency loop. An operation control unit is further configured outside the utility frequency loop and the variable frequency loop.