Based on the analysis of noise sources in the practical frequency-resolved optical gating (FROG) traces, a reasonable program to remove noises is designed. The direct reconstruction and the reconstruction after noise removing are conducted for the FROG traces with the analogue noises, respectively. The root-mean-square error of the latter is lower by one order of magnitude than that of the former, which confirms that this noise-removing program is effective. The FROG system is set up and the FROG trace of a practical pulse is obtained. By analyzing and comparing the results obtained from these two reconstruction ways, it is found that the reconstructed pulse obtained by the noise removing way is much closer to the real pulse, which verifies the necessity of noise removing.