As a load-side voltage regulating device, the back-to-back electric spring has the advantages of no energy storage element and low cost. However, the existing control methods don’t make full use of its operating domain. This paper takes the back-to-back electric spring as the research object and establishes the mathematical model of multiple working points of the spring. The operating domain of the spring is divided into four parts, and a corresponding segmented control strategy is proposed according to the characteristics of each operating domain. Piecewise control increases the running range of the spring, so that the critical load can still run at the rated voltage when the system voltage fluctuates, and the system can run stably. The simulation results of PSCAD/EMTDC also prove that the proposed piecewise control can make full use of the steady-state operating point of the back-to-back electric spring. This work is supported by the National Natural Science Foundation of China (No. 51877081).