This paper investigates the issues of topology design and capacity configuration in multi-microgrid (MMG) systems. Firstly, we analyze the limitations of current researches about MMG planning, which mainly focus on either topology design or capacity configuration separately, and propose the idea of joint planning simultaneously considering both aspects. Secondly, we present a two-stage stochastic optimization model aimed at minimizing the planning and operational costs to derive the solutions for topology design and capacity configuration. Moreover, various constraints are taken into account, including maximum equipment capacity, load shedding penalty cost, wind and solar power curtailment costs, and energy coordination among microgrids. Finally, simulation experiments are conducted using the islanded multi-microgrid (IMMG) as the research object, and additional comparative experiments are included to demonstrate the effectiveness and feasibility of the proposed model. Experimental results demonstrate that our method can significantly improve the economic benefits of MMG systems and enhance their penetration of renewable energy, which help promote the economic development and stable operation of MMG systems.