Aiming at the soft clay for foundation，we study the effects of recycled tire polymer fiber（RTPF）and glass fiber（GF）on the physical and mechanical properties of soft clay. We prepare the modified soil samples with different fiber types，fiber sizes and fiber contents，carry out the compaction test，unconfined compressive strength（UCS）test and direct shear test，analyze the variation rules of the indexes such as maximum dry density，UCS，cohesion and internal friction angle，and discuss the reasonable improved proportioning scheme. The results show that the incorporation of RTPF and GF decreases the maximum dry density，while the optimal water content increases. The incorporation of fiber is mainly to improve the shear strength of soft clay by increasing cohesion. There are critical fiber contents for RTPF and GF，which are 0.5% and 1.0% respectively. Beyond the critical content，the increase of fiber is unfavorable to the strength. Although RTPF may have better adhesion to clay than GF，its improvement effect is lower than that of GF because of larger diameter and smaller length-diameter ratio. Fiber size is also considered as an important factor for solidification.