<p>Silty soil in the floodplain of the Yellow River exhibits low strength and significant deformation due to its high porosity and compressibility, which restrict its use in roadbed engineering. This study identifies the optimal red mud-to-phosphogypsum ratio as 4:1, based on pH and unconfined compressive strength (UCS). Silty soil is stabilized using this ratio by adding red mud-phosphogypsum (R-P) and glass fibers, and the UCS is analyzed to determine the ideal content of R-P and glass fiber. Furthermore, the microstructure and chemical composition of the samples at the optimal ratio are examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR). The findings indicate that the optimal contents of R-P and glass fiber are 15% and 1%, respectively, resulting in a 55.2% increase in the UCS of the stabilized silty soil. In addition, microscopic analysis revealed the enhancement mechanism of the stabilized silty soil at the optimal ratio: red mud and phosphogypsum undergo a pozzolanic reaction, producing cementitious materials such as hydrated calcium aluminosilicate (C-A-S-H) and sodium aluminosilicate (N-A-S), which strengthen the bonding, embedding, and friction forces at the glass fiber-soil interface, reducing the post-peak strength attenuation by 71.6%. These research results can be a reference for the enhancement and utilization of silty soil, offering significant engineering application value.</p>