Abstract: The energy storage system with appropriate capacity for conventional units can effectively assist conventional units in primary frequency regulation and can improve the frequency characteristics of power system. This paper analyzes the frequency deviation and frequency change rate of the power system after primary frequency regulation, comprehensively considers the energy conversion efficiency and response time of all kinds of energy storage (namely, lead-acid battery, lithium iron phosphate battery, vanadium redox flow battery, and super capacitor) to set the capacity of energy storage, and establishes the economic benefit model of primary frequency regulation of conventional unit assisted by energy storage battery. Then, based on the cost structure and benefits of energy storage, the economy of energy storage participating in primary frequency regulation of power system under different control modes (namely, virtual droop control strategy, virtual inertia control strategy, hybrid optimization control strategy, and hybrid optimization control strategy considering dead band of energy storage) is evaluated. Finally, through simulation examples, it is concluded that different control strategies are suitable for different types of energy storage battery when the energy storage battery assists the conventional unit to carry out primary frequency regulation.