The multifunctional absorption/transmission structure exhibits significant potential for enhancing stealth capabilities and optimizing design quality in next-generation aircraft. This aligns with the prevailing trends in the functional and integrated development of future combat platforms. In this study, a novel metasurface-based sandwich rasorber is proposed. The design thoroughly considers the electromagnetic resonance mechanisms of the metasurfaces and the influence of the core layer thickness. Specifically, The lumped equivalent circuit of the metasurface resonant unit and the transmission line model of the structural layer are analyzed, and an equivalent circuit model of the complete sandwich rasorber is formulated. Utilizing this equivalent circuit model, a collaborative optimization method is developed to enhance the electromagnetic performances of the absorption/transmission sandwich rasorber. Calculations and simulation results demonstrate that the optimized sandwich rasorber achieves a low reflection band ( ) from 3.8 to 16.6 GHz, while maintaining a transmission band with an insertion loss as low as 0.26 dB at 10 GHz. These results validate the effectiveness of the proposed collaborative design method for the absorption/transmission sandwich rasorbers. Additionally, a systematic investigation is conducted to study the electromagnetic resonance mechanism and assess the influence of core layer thickness and dielectric constants on the electromagnetic performances of the sandwich rasorber. These findings offer important guidance for the optimal design and practical engineering of novel metasurface-based multifunctional composite structures.