With the ongoing advancements in equipment informatization and lightweight design, the development of navigation guidance and control (GNC) systems faces escalating complexity, while demands for system miniaturization and weight reduction grow increasingly urgent. System-in-Package (SiP), a high-density integrated packaging technology, addresses these challenges by encapsulating multiple functional chips into compact cavities, thereby achieving enhanced integration and system miniaturization. To meet the miniaturization requirements of GNC systems, this study presents a GNC information processing microsystem circuit designed using SiP technology. The circuit employs a DSP+FPGA architecture, integrates diverse interface and memory chips, and leverages mature ceramic substrate microsystem integration techniques. Comprehensive multi-physics simulations were conducted to validate the design. Experimental results demonstrate normal circuit functionality and full compliance with design specifications. Compared to the prototype verification board, the optimized circuit exhibits dimensions of 45 mm×45 mm×11 mm and a weight of approximately 60 g. Substituting traditional board-level systems with this circuit significantly improves product integration and fulfills critical miniaturization requirements for control systems.