Abstract: To effectively improve its weak engineering properties, the industrial by-product lignin is selected to improve the strength of the loess. The specific gravity, Atterberg limit, maximum dry density-optimal moisture content, and unconfined compressive strength (UCS) of the lignin-modified loess are tested by configuring the modified loess with different lignin contents. The engineering properties of the lignin-modified and the compacted loess are studied. The feasibility of the lignin-modified loess is discussed. Based on the results of the SEM, XRD, physical and mechanical properties tests, the reinforcement mechanism of the lignin-modified loess is analyzed. The results show that compared with that of the compacted loess, the specific gravity of the lignin-modified loess is significantly reduced. The liquid limit, plastic limit and plasticity index are reduced. Moreover, the maximum dry density and the optimum moisture content decrease. The lignin content and curing age significantly affect the engineering properties of the modified loess. When the curing age is 28 days and the lignin content is equal to 2%, the UCS of the modified loess is the highest, which is 32% higher than that of the compacted loess. The reinforcement mechanism of the lignin-modified loess mainly includes the interstitial effects of the lignin on the loess, cementation, clay mineral, ion exchange and electric double-layer adsorption.