A dynamic and adaptable method for choosing the time window and step size is given, based on the split-step Fourier method for solving the nonlinear Schrdinger equation. In this method, the time window is adjusted based on the diffusion of input pulse, and the step size is controlled by using a measure of the local error. This method has a high accuracy, which is most efficient for the improvement of calculation efficiency. How to choose positive and negative Fourier transformation forms during the calculation process is discussed, and how to get the approximate continuum waves in the time and frequency domain from the discrete results is analyzed. Supercontinuum generation in a high-nonlinearity photonic crystal fiber is investigated numerically, which validates the correctness of the calculation method.