Introduction   The paper aims to establish the profit model of generator-storage combined frequency regulation system and give the basis for battery storage power selection to determine the optimal capacity of battery storage.

  Method  Based on the historical operation data of a power plant and market price in Guangdong Province， we simulated the participation of battery storage in frequency regulation and analyzed the influence of battery storage power selection on the performance and income of combined frequency regulation.

  Result  The simulation results show that the battery storage system can greatly improve the frequency regulation income by enhancing the performance of the power unit and the mileage. With the increase of the battery storage power， the frequency regulation income gradually increases and then tends to be stable.

  Conclusion  The impact of battery storage power on the performance and income is different due to the unit performance differences and operating conditions. This work provides that it is reasonable and feasible to determine the battery storage capacity through simulation calculation， which can provide reference for the optimization of battery storage capacity in subsequent projects.