Abstract: The electricity-natural gas coupling system consisting of gas generation units and power to gas（P2 G） facilities improves the interaction of different energy systems. In order to realize the safe and economic operation of the coupling system during planning year, an optimal planning method for electricity-gas coupling system considering P2 G is proposed, which aims at minimizing the sum of annual investment cost and annual operation cost. This optimization method can obtain the construction state of gas generation units, P2 G plants, power lines, gas pipelines and optimal output of typical daily gas generation units and P2 G plants in the planning year. Then, based on the proposed method, 7-node natural gas and 9-node power system can be modeled and calculated in different scenarios. Finally, the results of immune algorithm show that the reasonable location planning for P2 G plants can reduce the construction cost of natural gas network pipeline, and the output adjustment of gas generation units and P2 G plants can reduce the operation cost of the system.