Abstract: Along with the low-carbon transformation of the new power system, the proportion of installed renewable energy surges, and the cross-seasonal power and electricity balance between the load and renewable energy further promotes the demand for long-term flexibility. The long-term energy storage has become an emerging capacity resource to maintain the long-term capacity sufficiency of the system. The long-term energy storage has not been considered in the existing capacity cost payment mechanism for the traditional power generation units, so the economic drive for the development of the long-term energy storage is insufficient. Aiming at the mechanism design of the appropriate capacity payment for the long-term energy storage system, a planning scenario reduction method for the variable period time series is proposed based on the dual-granularity time grid structure containing intra-period and inter-period, and a capacity optimization model for the long-term energy storage is established to measure the capacity payment demand. Combined with a case of a renewable energy enrichment region, the validity of the calculation model of the long-term energy storage capacity and payment level is verified. Based on the sensitivity analysis of critical factors, the declined evolution trend of the capacity payment demand for the long-term energy storage is discussed, which provides a reference for the capacity payment mechanism design to promote the sustainable development of the long-term energy storage.