Abstract: Palm fiber combined with microbial-induced carbonate precipitation (MICP) technology was employed to synergistically improve the clay soil collected from a first-class highway construction site in Huanggang City, Hubei Province. Unconfined compressive strength (UCS) tests were conducted to investigate the variations in clay strength with fiber length, fiber content, and curing time before and after improvement, and the effects of different improvement methods on the mechanical properties of clay were compared and analyzed. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and calcium carbonate content measurements were performed to observe the microstructure, analyze the mineral composition, and determine the amount of mineral precipitation, thereby revealing the improvement mechanism of the MICP-palm fiber composite-treated soil.The results show that the MICP-palm fiber composite-improved soil significantly enhances the UCS of clay. During curing periods of 7, 14, and 28 days, the UCS exhibits an increasing trend with prolonged curing time, reaching its maximum value at 28 days. With increasing curing time from 7 to 28 days, the dominant mechanism of strength enhancement transitions from fiber reinforcement alone to a combined improvement by both MICP and fiber reinforcement, with the MICP effect becoming more pronounced. An appropriate amount of fiber provides additional attachment sites for microbial colonization. The optimal fiber content and length under this combined scheme are 0.2% and 12 mm, respectively, achieving an approximately 122% increase in UCS compared to the untreated soil. The research findings provide a valuable reference for the development of green and low-carbon engineering practices.