In this paper,a method of twice sampling based on split-step Fourier method was developed to analyze and simulate the supercontinuum generation in photonic crystal fiber pumped by sub-nanosecond laser pulse. Applying this method to generalized nonlinear Schrdinger equation,much operation time was saved in Supercontinuum simulation,and the simulated spectrum agrees well with the experimental result under the same conditions. Also,the slight dissimilarities between the simulated spectrum and the experimental one were discussed. The simulated supercontinuum with 1.15W power generated in 1.8 m Photonic Crystal Fiber and the evolution of spectrum by our work can give reference for improving further experiment setup.