The field test of single pile under horizontal load is carried out on the artificial fill foundation with large thickness. The load-displacement relationship, rotation angle and bending moment of the ground are measured, and the law of pile-soil interaction under horizontal load is revealed. The variation law of the proportional coefficient m of the horizontal resistance coefficient of foundation soil with load and displacement is also explored. The results show that the horizontal critical load of pile foundation is 480 kN, and after reaching the critical value, the horizontal displacement and rotation angle of pile foundation change suddenly. The bending moment diagram of the pile foundation shows a distribution pattern of " small at both ends and large in the middle ". The influence range of the bending moment along the depth is about 10 m, and the proportional coefficient of the horizontal resistance coefficient decreases exponentially with the increase of load and displacement. The results of m method are verified and improved by experimental data. It is found that the maximum displacement calculated by m method is close to the measured results. The calculation of bending moment when the load exceeds the critical load is quite different, compared to the correction coefficient function β, the m method is improved.……