A method was developed for nonlinear analysis of laterally loaded long piles in cohesionless soil. It is considered that the modulus of horizontal subgrade reaction is related with groundline pile displacement by an attenuation power function based on the existing methods and it is assumed that both the modulus of horizontal subgrade reaction and the ultimate soil resistance increase linearly with depth . It is also considered that soil in front of the pile may change from elastic state into plastic state as pile displacement increase. Nonlinear differential equations of the fourth order were derived for both states and to solve the equations, the Gleser finite difference approach with iteration and the ReeseMatlock approach were developed,respectively of propsed methed. It is validated by the test and numerical field calculation that the results respectively of proposed methed are more accurate than ‘m’method and simpler than ‘py’method. And the results are in good agreement both when pile displacement is small and large,thus it can be applied to construction in place of ‘py’ method especially when test parameters are unavailable.