In order to decrease the limit of detection of elements and improve signal-to-background ratio (SBR) and the stability of characteristic spectral lines of laser-induced breakdown spectroscopy (LIBS) of heavy metals in soil, we study the polarization property of four characteristic discrete spectral lines of Fe, Pb, Ca, Mg elements and continuous background radiation of LIBS in soil, and analyze the limit of detection, SBR and relative standard deviation (RSD) of characteristic spectral lines of elements under the conditions of polarization and no-polarization. The results indicate that the polarization degree of four characteristic spectral lines Fe Ⅰ: 404.581 nm, Pb Ⅰ: 405.780 nm, Ca Ⅰ: 422.670 nm, Mg Ⅰ: 518.361 nm and corresponding continuous background radiation are 0.27, 0.17, 0.25, 0.23 and 0.70, 0.64, 0.69, 0.67, respectively. The polarization resolved LIBS (PRLIBS) technology makes RSD of four characteristic spectral lines Fe Ⅰ: 404.581 nm, Pb Ⅰ: 405.780 nm, Ca Ⅰ: 422.670 nm, Mg Ⅰ: 518.361 nm decrease by 3.28％, 2.2％, 3.24％ and 1.34％, respectively. Continuous background radiation is effectively depressed by PRLIBS technology, and SBR of four characteristic spectral lines is increased by 5.59, 5.67, 5.30, 7.35 times, respectively. Under the conditions of polarization and no-polarization, the limits of detection of heavy metal Pb are 17.4×10-6 and 39.4×10-6, respectively, limit of detection under polarization is 44% that of non-polarization. Above results provide data support for further improving quantitative analysis ability of LIBS on heavy metal in soil.