Abstract: To address the problems of overcharge and overdischarge, excessive cycling depth, and accelerated lifetime degradation of battery energy storage systems participating in primary frequency regulation, a control method that balances frequency support performance and battery lifetime preservation is investigated. Neglecting the internal nonlinear characteristics of the energy storage system, an external dynamic model and an energy capacity model for primary frequency regulation are established. Based on the nonlinear relationship between cycle depth and cycle life, a lifetime degradation model is developed, and the Dambrowski counting algorithm is employed to identify charge–discharge cycles and quantify their depth from the state-of-charge sequence. On this basis, by considering the trade-off between frequency deviation and lifetime degradation, charge–discharge depth thresholds are determined and an adaptive frequency regulation coefficient is designed to achieve dynamic adjustment of the storage output. A power system frequency response simulation model is built in Python, and comparative studies are carried out among the proposed strategy, the case without energy storage, and the fixed frequency regulation coefficient strategy. The results show that the proposed control strategy can effectively suppress the lifetime degradation of the energy storage system while satisfying the requirements of primary frequency regulation, thereby improving the stability and coordination of the system frequency response.