Epoxy-based sandwich composites with improved economic efficiency were developed to better utilize composite components with functions such as high mechanical performance and light weight, which influenced quality for load-bearing applications. Herein, an epoxy-based sandwich composite was made by laminating woven basalt fibers (WBFs) as a face sheet on 3D carbon felt foam (3D CFs) as a core material. The cast-in-place process was used to infuse the epoxy solution within the sandwich, resulting in bicontinuous composites with outstanding mechanical characteristics and high performance. In addition, the epoxy solution was combined with a silane coupling agent to boost the composite’s toughness by enhancing the adhesion between the fibers and the epoxy. The mechanical properties of epoxy composites were also found to be much improved when WBFs were used as a face on 3D CF foam. Compared to the epoxy/3DCFs/WBFs composite sandwich to pure epoxy, the flexural and tensile strengths improved by 298.1 and 353.8%, respectively, while the impact strength rose to 135 kJ/m². This research shows a new way to make a new process for making sandwich composites with epoxy that is cheap and strong.