Half screw pile technique has been applied in many kinds of projects. However， due to the limitations of cognitive conditions and the complexity of research objects， the theoretical analysis is still lagging behind the engineering practice. The particle flow code based on discrete element method was used to establish the numerical analysis models of vertically loaded half screw piles， the microscopic parameters of the models were verified by the existing experimental results. On this basis， the effects of the design parameters such as screw spacing， length of the threaded section and external diameter on the bearing characteristics of the half screw piles were analyzed. The research results show that the ultimate bearing capacity of the half screw pile reaches maximum and then decreases with the increase of screw spacing， the half screw pile has the best bearing performance where the screw spacing is （1.0-1.33） D， the load sharing ratio of the threaded section is the highest，while the straight section is the lowest. The ultimate bearing capacity of the half screw pile increases linearly with the increase of the length of the threaded section， and then basically remains unchanged，and it is suggested that the reasonable length of the threaded section is generally not more than 2/3L. With the increase of external diameter， the ultimate bearing capacity of the half screw pile is approximately linear and increasing rapidly. The numerical simulation results can provide some theoretical references for optimizing the design parameters and establishing the bearing capacity estimation method of the half screw pile.