In order to improve the accuracy of quantitative analysis of laser induced breakdown spectroscopy (LIBS) technology, the research on the detection of heavy metal elements in soil by LIBS technology under the confinement of magnetic field was carried out,and the data were processed by multi spectral line intensity normalized internal standard method.By comparing the spectral characteristics when the magnetic field intensity was 0 T,0.3 T,0.8 T and 1.25,respectively,it was obtained that the spectral intensity and signal-to-noise ratio (SNR) increased with the increase of magnetic field intensity. When the magnetic field intensity was 1.25 T,the spectral intensity and SNR of Cd and Cu were 34.77%,56.33%,40.83% and 74.12% higher than that without magnetic field,respectively.The quantitative analysis model of Cd and Cu was constructed when the magnetic field intensity was 1.25 T.The results showed that compared with the traditional internal standard method,the element detection limits of the multi spectral intensity normalized internal standard method were reduced from 52.78 mg/kg and 49.18 mg/kg to 23.87 mg/kg and 18.06 mg/kg,respectively.The correlation coefficients increased from 0.961 3 and 0.942 7 to 0.996 9 and 0.999 3,respectively.In this experiment, the spectral characteristics of LIBS are improved,the accuracy of quantitative analysis is improved,and the detection limit and measurement error of heavy metals are reduced by using the multi spectral line intensity normalization internal standard method.