Abstract: A series of problems, such as low-order polynomial fitting with lower accuracy, high-order polynomial fitting with no convergence, five-point smoothing method countering unequally spaced data and so on, may occur in the data processing for laterally loaded trial piles, which impedes the application of the test data. To overcome the difficulties as discussed above, firstly, this work obtains Akima nonlinear polynomials for the measured data by the piecewise polynomial fitting technology on the basis of Akima nonlinear interpolation theory. Moreover, integral and difference expressions for the corresponding nonlinear polynomials are derived to establish the data processing method for laterally loaded trial piles based on the Akima interpolation theory. For the results oscillating from the data processing, the filtering method will be employed to deal with this issue. Finally, one case study for flexible piles is performed to illustrate the application of the proposed data processing method. Comparison shows that the results from proposed method are almost identical to those of theoretical calculation, which verifies the reliability and practicability of this new method. This study may provide a new approach to solve the difficulties in data processing for laterally loaded trial piles.