In order to realize the large-scale and normal implementation of power-to-gas technology, as well as the large-capacity storage and long-distance transportation of gas in the later stage of electric hydrogen production, a power-to-gas technology with real-time energy conversion characteristics and large-scale energy storage characteristics is studied in this paper. Firstly, the water-electricity-gas coupling process between the electrolytic cell and the methanation reactor in the power-to-gas system is discussed in detail, and the model of the power-to-gas system based on the coordination of real-time energy conversion and large-scale energy storage is proposed. Then, based on a multi-energy coupling regional integrated energy system, a highly decoupled multi-step modelling method is adopted to construct its optimal operation model, and the equivalent variable substitution method is used to transform it into a linear programming problem. Finally, the calculation results show that the proposed power-to-gas technology can further improve the energy utilization efficiency due to the complementary characteristics of the two functions, so as to effectively promote the implementation of large-scale power-to-gas projects in the future.