Large-mode-area photonic crystal fiber is used to generate high power, high beam quality supercontinuum. Propagation and supercontinuum generation process of laser pulse in large-mode-area (LMA) photonic crystal fiber (PCF) is simulated by solving the general nonlinear Schrdinger equation (GNLSE) using the split-step Fourier method. Effects of the pump pulse parameters (peak power and chirp) and the length of photonic crystal fiber used on supercontinuum generation are particularly estimated. Nonlinear spectral broadening mechanism of laser pulse in large-mode-area photonic crystal fiber is discussed. The results show that the process of supercontinuum generation can be divided into three stages: initial broadening, dramatic broadening and saturation broadening. The spectrum width and efficiency can be achieved by the optimized length of LMA PCF to insure output of the generated supercontinuum at the dramatic broadening stage. The pump peak power and chirp have important impact on supercontinuum generation. When a small peak power pump is input, the spectrum broadens symmetrically. When the pump peak power increases, it brings little changes with the shorter wavelength component but broader of the longer wavelength component. The time-domain shape of the pulse exhibits concussion modulation as the effect of pulse breakup. When the pump chirp is positive, little influence is shown, except a shift of longer wavelength power by increasing the chirp. But the full width of the supercontinuum has little changes. While the pump chirp is negative and satisfy certain condition, the nonlinear is enhanced to facilitate the supercontinuum generation.