Abstract: In order to study the influences of the ultimate frictional resistance of the backfill on the bearing characteristics of piles, the method for calculating Q-S curve of piles with exponential load transfer equation is obtained by considering the nonlinear change of the ultimate frictional resistance of backfill under low confining pressure. This method is validated by combining the existing research results and engineering practice results, and the influences of parameters of the ultimate frictional resistance on bearing characteristics of piles are discussed. The results show that the side resistance of the rock-socked section first reaches the extreme value. The normal stress σ and the test parameters A and b of the material are very beneficial to improve the side resistance and the ultimate bearing capacity of piles. Especially, the influences of the normal stress σ on the side resistance and the ultimate bearing capacity of piles are obvious.