This study aims to experimentally analyze the effect of fiber length and fiber content on shear strength and deformation properties of fiber reinforced soil by consolidated-undrained triaxial shear tests. The best mechanical properties are presented by the samples with 1.0 % fiber content and 3.09 cm fiber length. The stress-strain relationship of fiber reinforced soil is strain hardening. The change laws of pore water pressure with the increasing of axial strain are affected by both confining pressure and the void ratio. The effective stress paths of fiber reinforced soil move to the left of the p’- q surface with the increase of fiber content, and the fiber length has no significant effect on effective stress paths. Reinforcement effect mainly improves the cohesion of soil samples, and three distribution patterns of flexible fibers in soil are proposed. The failure mode of saturated cotton fiber reinforced soil is bulging failure, radial deformation of soil is obviously restrained by fiber reinforcement.