A portable laser-induced breakdown spectroscopy system based on fiber laser was developed to meet the demand of rapid detection in industrial field and rugged environment. A algorithm of background removal based on iterative wavelet transform was used to eliminate the high continuous background interference caused by the high repetition rate of the fiber laser. The emission lines of element Mn in pig iron samples were compared before and after the background removal. After background removal by the iterative wavelet transform algorithm, the determination coefficient of calibration curve for four emission lines of element Mn was improved from 0.988, 0.985, 0.982 and 0.992, to 0.994, 0.994, 0.994 and 0.995, respectively, and the root-mean-square error of cross-validation was decrease from 0.123, 0.146, 0.101 and 0.083, to 0.072, 0.085, 0.062 and 0.073, respectively. The results show that the algorithm of iterative wavelet transform can effectively remove the continuous background interference, improve the accuracy of regression model, and then improve the accuracy of quantitative analysis.