The technology of power to hydrogen (P2H) and natural gas mixed hydrogen is highly regarded in theoretical research and engineering application in promoting the consumption of renewable energy and reducing carbon emissions. Targeting the park integrated energy system with high proportion renewable energy, an optimal configuration method of P2H considering natural gas mixed with hydrogen and cross seasonal storage is proposed. Firstly, the operational framework and energy flow relationship of the park integrated energy system are sorted out, and the mathematical models for the internal energy production, conversion, and storage equipment in the park are established. Secondly, a configuration model of P2H is established with the goal of optimizing the annual investment cost of equipment, the annual operating cost, and the carbon trading cost. Finally, the effectiveness of the proposed model is verified by an example analysis. The impact of changes in investment cost of electrolytic cells, the upper limit of mixed hydrogen volume fraction and cost weight coefficients of economy and low-carbon on the planned operation results are analyzed. The simulation results show that the proposed model can effectively improve the absorption capacity of renewable energy and reduce the overall economic cost and carbon emissions.