The nutrient elements in the soil are quantitatively detected by laser induced breakdown spectroscopy (LIBS). The Nd∶YAG pulsed laser with output wavelength of 1064 nm and pulse width of 5.82 ns is used as light source to focus on the surface of the soil to generate laser induced plasma. The plasma emission spectra are measured with utilization of a three grating spectrometer and a gate width controlled intensified charge-coupled device (ICCD). On the basis of traditional LIBS system, beam expander system and real-time monitoring system are added to form LIBS system with cage structure. The focusing position of laser in LIBS system with cage structure is optimized, the optimum laser focusing position is 0.2 cm. The signal intensities of Mg II 279.56 nm, Mg II 280.26 nm and Mg I 285.21 nm spectral lines are tested. The results show that the LIBS system with cage structure is superior to the traditional LIBS system in signal stability. The detection limits of Cu, Mn, Mg and K elements in soils are 0.42×10-6, 13.2×10-6, 38.5×10-6, 62 ×10-6, respectively, which are better than the detection limits obtained by traditional LIBS system. The mass fractions of Cu, Mn, Mg and K elements in soils are predicted based on the calibration model, the average relative errors of the elements are 9.2%, 9.6%, 8.5%, and 10.9%, respectively.