Abstract: In this paper, a novel two-stage distributionally robust optimal planning model for electricity-heat-hydrogen-ammonia coupled microgrid is proposed, incorporating an electrothermal-aging model to precisely simulate the aging effect of solid oxide electrolysis cell (SOEC) and to enhance the system energy efficiency. Furthermore, the model formulates a multi-energy coupled system through the cascade utilization of thermal energy. The planning model employs a Wasserstein-based ambiguity set to minimize the total investment and operating costs while accounting for the uncertainty in wind power. Case studies verify that, compared to models lacking distributionally robust methods, SOEC electrothermal-aging effects, or cascade thermal energy utilization, the proposed model enhances energy utilization efficiency while fully leveraging wind power, demonstrating high flexibility and economic viability.