In order to explore the horizontal bearing characteristics of pile foundations in large‐thickness artificial fill foundation and the applicability of the m‐method in engineering practice, the field tests of horizontal bearing capacity of single piles and the theoretical calculations of the m‐method are carried out. The variation patterns of displacement and bending moment under horizontal loads are obtained, and the deformation characteristics of pile-soil under horizontal loads are presented. The variation of the proportional coefficient m of the horizontal resistance coefficient of the foundation soil with the load and displacement is further obtained. The results show that with the increase of loading, the horizontal displacement increases continuously, and after reaching the critical value of 480 kN, the horizontal displacement and displacement gradient of pile foundations change drastically. Under the same loading, the bending moment of pile foundations increases first and then decreases with the increase of depth. The bending moment diagram shows the distribution pattern of “small at both ends and large in the middle”. At the same depth, the bending moment increases with the increase of load, and negative bending moment appears at a certain depth. The influence range of bending moment along the depth is about 10 m. The proportional coefficient m of the horizontal resistance coefficient decreases exponentially with the increase of load and displacement. When the load and displacement are small, the m values of the two piles are quite different. When the load and displacement increase to a certain value, the m values of the two piles are close and finally stabilized near a specific value. The calculation results of the m‐method are verified and improved by experimental data. It is found that the maximum displacement calculated by the m‐method is close to the measured results. When the load is small, the calculated maximum bending moment is close to the measured results. After exceeding the critical load, the difference is large, indicating that when the load exceeds the critical value, the maximum bending moment does not show a linear elastic increase. It is necessary to correct the bending moment calculation result by the correction coefficient function β. The corrected bending moment is more consistent with the measured value, indicating that the m‐method works well in engineering practice.