Abstract: It is a common engineering method to improve the subgrade soils in seasonal frozen soil areas. Lignin fiber is an economical and environmentally friendly additive with good durability. Taking the soils improved by the lignin fiber as the research object, the UU triaxial tests and SEM scanning tests are carried out on the soil samples with different contents of lignin fiber after freeze-thaw cycles. The influences of the times of freeze-thaw cycles and the content of fiber on the mechanical properties of the soils are analyzed emphatically. The results show that the characteristics of stress-strain curve are related to confining pressure, freeze-thaw times and lignin fiber content. The elastic modulus, strength and cohesion of the reinforced soils decrease with the increase of freeze-thaw cycles. Under the lignin fiber content of 0.75%, the elastic modulus, strength and cohesion of the reinforced soils reach the maximum. The fiber forms a three-dimensional grid structure in the soil samples or plays a role of "bridge" overlapping, which reduces the impact of freeze-thaw on the pore damage, thus enhancing the strength of the soils. The test results show that the reinforced soils with lignin fiber have obvious advantages in resisting repeated freeze-thaw cycles.