Abstract: In order to obtain the behaviors of horizontal bearing capacity of large-diameter belled concrete piles, numerical simulation using FLAC^3D software is carried out for analyzing the factors affecting the bearing capacity. First, the simulated results and field test results are compared to verify the reliability of the simulation model, and then the soil depth, soil elastic modulus, belled head size and main factors affecting the horizontal bearing capacity are simulated and analyzed. The results show that the elastic modulus of the upper layer soil is significant to affect the horizontal displacement of large-diameter belled piles and should be above 10 MPa. In order to give their full play of horizontal bearing capacity, the pile length should be around 7 times the diameter and not be greater than 10 times the diameter. The horizontal bearing capacity, economy and construction techniques are taken into account, and the ratio of the belled head height to the diameter should be between 0.5-0.7. The results have some practical significance for guiding engineering practice.