Abstract: The distribution of the coefficient of subgrade lateral reaction is usually assumed to be a slope linear with depth. The slope coefficient of subgrade reaction is termed as m value. The m value can only be gained from the empirical range in the table of the codes which are too crude and have not been renewed for 30 years. Combing the p-y curve with the m method, the relationships among undrained shear strength c_u, pile diameter and m value of saturated clay are established in the case of the same displacement of piles on the ground surface when the distribution model of c_u value increases or is constant with depth. The results can be expressed in the form of simple tables and formulae with convenience. If c_u value along depth is trapezoid, it can be considered as the super position of the above basic models. The stiffness of pile shaft has little influence on the above relationships. The allowable bearing capacity or relevant displacement of piles obtained by the suggested m value is in accordance with the test results of two practical cases. The proposed method provides a more comprehensive and reasonable?way to determine the m value.