The invention provides a measurement method for measuring the energy state operation interval of a battery string. The method comprises the steps of conducting the constant-power discharge test on a battery string, determining the lower limit of the energy state operation at the constant power according to the voltage changing rate of the battery string and the battery voltage range, conducting the constant-power charge test on the battery string, determining the upper limit of the energy state operation at the constant power according to the voltage changing rate of the battery string and the battery voltage range, and determining the operation interval of the energy state of the battery string according to the lower limit of the energy state operation and the upper limit of the energy state operation. According to the technical scheme of the invention, through measuring the voltage of the battery string during the charging/discharging process and the battery voltage range, the operation interval of the energy state of the battery string at one power can be analyzed and obtained for the evaluation on the energy state operation interval of the available power of an energy storage unit. Therefore, the method provides a technical means for evaluating the charge and discharge capability of the energy storage unit. The above parameter (energy state operation interval) has an important significance on the accurate control of the energy storage unit and an energy storage power station.