In the field of shoe materials, natural rubber (NR) is widely used due to its irreplaceable anti-slip performance. Considering the increasing demand for lightweight shoe materials, hollow microsphere (HGM) is recognized as an ideal weight-reducing filler, due to its low density, low cost, and high strength. However, the inherent chemical inertness of HGM makes it difficult for conventional coupling systems to regulate the interfacial compatibility between HGM and the rubber matrix, resulting in a decrease in the mechanical properties of the composite materials. In this study, a hydrothermal activation method was employed to increase the surface roughness and the number of active hydroxyl groups on the surface of HGM. This allowed the silane coupling agent KH550 to be efficiently grafted onto the surface of HGM and enhanced the interaction between HGM and NR. Under the combined effects of hydrothermal activation and coupling modification, HGM achieved improved compatibility with NR. The lightweight rubber material prepared in this way exhibited a tensile strength of 9.26 MPa and a tear strength of 45.49 N/mm, with a specific gravity of 0.89. Herein, this study not only achieved the lightweight modification of NR but also endowed HGM with reinforcing effects, providing a new strategy for the multifunctional application of HGM and the development of new types of shoe materials.