The growing demand for communication, sensing, and computation, as well as the increasing constellation sizes of SGINs, has attracted much attention. This chapter elaborates on the applicability and future development trends of the SGIN from the perspective of mega-satellite constellations. With the growth of network scale, some characteristics remain unchanged, and problems can be solved through current methods. However, with change, this will not always be the case, which will require the analysis of network changes and the modeling and optimization of SGINs with mega-satellite constellation characteristics. This chapter provides a theoretical foundation and guidance for future design, optimization, and deployment.