Abstract: This paper systematically investigates the physical and mechanical properties of loess improved by urea enzyme-induced calcium carbonate precipitation (EICP) technology and lignin fibers, both individually and in combination, through physical property measurements, unconfined compression tests, and microstructural analysis. Results show that: EICP solution significantly increases the pH value of loess, while lignin fibers effectively reduce its alkalinity. Individually, both EICP solution and lignin fibers increase the electrical conductivity of loess, but their combined application with 0.5% lignin fibers can notably decrease conductivity. EICP technology fills pores and cements particles by calcium carbonate crystal formation, achieving a compressive strength of 382.2 kPa at a 6% solution content; lignin fibers (1% content) enhance strength by 38% through bridging effects. Their synergistic improvement significantly enhances soil structural strength and initial stiffness, improving initial deformation resistance under load. The optimal combination (0.5% lignin fibers + 6% EICP) exhibits a compressive strength of 425.5 kPa, showing a significant improvement compared to unimproved loess. Microstructural analysis reveals that the fiber network and calcium carbonate crystals jointly fill pores and form a dense structure after combined improvement, effectively inhibiting crack propagation. This study elucidates the synergistic improvement mechanism of EICP and lignin fibers, providing theoretical support for the development of green geotechnical engineering materials.