In this paper, the effect of ambient pressure (between 1.01×105 and 1×102 Pa) on soil plasma radiation and element detection limit was studied by using Nd∶YAG laser to induce soil plasma. The research shows that the spectral intensity of soil plasma and the signal-to-background ratio increase first and then decrease with decreasing pressure, and the both maximum value are 1.69 times higher at 8×104 Pa compared with normal pressure; In addition, the electron density also increases first, then decreases, and reaches a maximum of 3.56×1016 cm-3 at 8×104 Pa. Induced plasma emission spectrum has good stability and high precision at 8×104 Pa compared with normal pressure. The relative standard deviation of the signal intensity of soil plasma analysis line is 1.1%, which is significantly lower than 3.5% at normal pressure, and the stability of plasma emission spectrum is significantly improved at low pressure. Besides, the internal standard method was used to determine Pb content in soil, and the limit of detection of Pb in soil is 57.27 mg·kg-1 at 8×104 Pa, which is 39.23 mg·kg-1 lower than the limit of detection at normal pressure. The results of the study shows that spectral detection sensitivity of laser-induced breakdown spectroscopy can be improved effectively in the appropriate low pressure environment. The appropriate low pressure environment can improve the detection limit of elemental analysis and increase the accuracy and precision of spectral quantitative analysis.