Abstract: The m method is a common method to analyze the deformation and internal force of laterally loaded piles. In the absence of test piles, the ratio coefficient m value of lateral resistance coefficient in the m method can only be taken from a wide range recommended by the relevant code according to the type of foundation soil, etc., highly dependent on engineering experience and random. Main soft soils along Shanghai-Nantong Railway are classified into 11 subcategories according to the compression characteristics. The influences of horizontal force H, horizontal displacement$Y_0$ of mud surface (pile top), pile diameter D and soil compression index$C_{\text{c}}$ on m value are analyzed through the numerical test method. The fitting relation between m and$C_{\text{c}}$ and the relation between m and$Y_0$ are established through statistical analysis, and are verified by the field horizontal static load tests. The results show that the m value decreases with H,$Y_0$ and$C_{\text{c}}$, and the attenuation speed decreases continuously. D has a certain influence on the m value, corresponding to the best diameter of pile D=1.25 m. The fitting formula for m value corrected by the field tests is reliable and can be fine-tuned according to the deformation parameters of soils.