The invention provides a photovoltaic energy storage battery frequency modulation method based on a direct current side. The method comprises the steps of configuring a set of energy storage battery for each photovoltaic inverter in a photovoltaic power station, wherein the energy storage battery is connected with the corresponding photovoltaic inverter and each photovoltaic module for charging the corresponding photovoltaic inverter through an energy storage bidirectional DC/DC converter. When frequency disturbance occurs in a power grid, active power output of the photovoltaic inverter is adjusted by adjusting charging and discharging power of the corresponding energy storage bidirectional DC/DC converter preferentially. In the invention, through charging of the energy storage battery, the active output of the photovoltaic inverter is reduced under a condition that output power of the photovoltaic module is not discarded; through discharging of the energy storage battery, the activepower output of the photovoltaic inverter is improved under the condition that a maximum power point operation mode of the photovoltaic inverter is not changed. Therefore, the photovoltaic inverter can be operated at the maximum power point as much as possible so as to ensure full utilization of power generation of the photovoltaic module.