Abstract: The load-settlement function of a screw pile under axial load was built on the bilinear model of soils and the transferring process of force from the pile to ground,and some solutions to this transfer function were educed.Through the fitting of 6 curves of load-settlement(P-s curve) obtained by static load tests on the continuous kind and the bed kind of screw piles,the ultimate capacity of screw piles could be estimated by the method of s-logP,and the rational design value of capacity of a single pile was proposed.