Abstract: The pile-soil interaction was observably affected by the geometrically complex shape of screw pile, and the analysis of this problem was helpful to explain its pullout characteristics. On the basis of bearing capacity theory of deep foundation, the bearing capacity characteristics of pullout screw pile foundation were investigated, and the modificatory RDD (the ratio of the laminas distance to the net radius of lamina) was proposed. By 12 model pullout tests of screw pile with 3 RDDs, the soil stresses during the pullout process were measured, and the load-transfer mechanism was investigated. The pullout test results show that (1) the stress dispersion in lamina-soils is less for RDD<5; (2) the load-transfer in lamina-soils occurs along the outer perimeter of laminas for RDD<3; (3) for RDD=5, the pile-soil interaction of pullout screw pile foundation is significant, and the slide failure may occur at the ground above the first layer lamina.