The present invention discloses a battery energy storage system economic model assessing from a power grid side and a new energy power plant side separately. The model is used for assessing the economical efficiency of investing a battery energy storage system to promote the commercialized application and development of the system. The model comprises a power grid side model and a new energy powerplant side model. The power grid side model comprises five aspects of benefits such as low-storage and high-discharge interest arbitrage, reduction of conventional reserve capacity, reduction of power grid outage loss, reduction of power grid network loss and delay of power grid upgrading investment, and two parts of cost such as investing construction and operational maintenance. The new energypower plant side model comprises four parts of benefits such as reduction of new energy power-generation spinning reserve capacity, reduction of construction capacity of new energy grid-connection channel, environmental benefit of reduction of carbon emission and the low-storage and high-discharge interest arbitrage under hypothetical peak and valley generation prices. According to the model, comprehensive and quantified analysis is perform on the benefit of the battery energy storage system based on different investment subjects, so that the deficiencies, such as incomprehensive benefit analysis and difficulty in calculation, of the conventional model are compensated.