Abstract: Under the market environment, it is of great significance for the development of energy storage industry to build a market mechanism that fully reflects the characteristics of energy storage. Energy storage has an elastic demand for the energy state. However, in the current market mechanism it is inconvenient for the energy storage part to declare this transaction intention, failing to give full play to the flexibility of the energy storage. Thus, an operation mode of energy storage based on the flexible state of energy is produced, which is characterized by relaxing the constraints of energy state at the end of the optimization period, thus increasing the benefits of energy storage in the market. In this paper, the principle and characteristics of the operation mode of the flexible state of energy are systematically described, the new corresponding quotation mechanism for the day-ahead energy market is designed, and the market scheduling model is established. This mechanism allows the energy storage part to declare the demand curve describing the states of energy and its charge and discharge costs, while the system operator determines the energy storage's time-of-use charge and discharge power and its final state of energy during the clearing. Finally, an example is given to prove that the new mechanism can maximize the social welfare, reduce the market risks, and improve the benefits of energy storage.