Beam pumping motor system (BPMS) is a typical periodic potential energy load which is affected by factors such as down-hole load, mechanical transmission and geological structure. During a running cycle, the power fluctuates in a large range and multiple operating conditions where potential energy, electrical energy and kinetic energy are converted to one another and thus leads to lower system efficiency. For this type of load, a four-quadrant inverter is an effective method to improve the efficiency of the motor system. However, in practice, the two-quadrant variable frequency control is widely used due to its lower cost. The drawback of this control is the difficulty in realizing efficient conversion and utilization of electrical energy under the power generation mode, since the generated electrical energy is converted into thermal energy by the installed resistance brake inside the inverter, which causes additional energy consumption. To resolve this problem, this paper systematically studies the influence of frequency regulation on the load torque of BPMS, an automatic tracking frequency regulation method is then proposed. With this method, the controllable conversion between the kinetic and potential energy forms can be realized, and the fluctuation power under dynamic load conditions can also be smoothed. Meanwhile, energy consumption in power generation mode is also reduced effectively. The correctness and practicability of the proposed method are verified by the simulations and experiments of a standard oil well. The results show that, comparing to the traditional two-quadrant inverter, the proposed method can reduce the active power fluctuation of the system by about 20% under the premise of still using a two-quadrant inverter, and the power saving ratio is increased by more than 10%.