The autocorrelation characteristics of the noise-like pulse generated from fiber laser are investigated using numerical analysis. Numerically calculated autocorrelation traces agree with experimental results. By changing the parameters, it is found that the pedestal and the spike reflect the average pulse width and intrapulse width, respectively. Increasing intra- pulse number in a noise- like pulse leads to a smaller spike- topedestal intensity ratio, while the width of the pedestal and the spike are not obviously influenced. Numerical analyses show that the contrast ratio of the interferometric autocorrelation trace less than 8∶1, which is detected in experiment, is determined by the noise-like pulse width ,pulse chirp and scan range.