Based on the external cavity constraint method, the experimental parameters of laser induced breakdown spectroscopy (LIBS) of Al and Si in bauxite were optimized. By setting the pressure, laser energy, delay time and other parameters, traditional LIBS and external cavity constrained LIBS (CC-LIBS) were used to ablate bauxite samples. The optimal experimental conditions were analyzed by selecting SiⅠ288.15 nm and AlⅠ308.21 nm as the characteristic spectrum. The results show that: when the pressure is 150 MPa, the deviation of the spectral line intensity is the smallest; when the energy is 80 mJ, the collected characteristic spectral line SNR is the largest; when the delay time is 1 μs, the SNR obtained by the two elements of Al and Si is the best, the optimal experiment condition is determined. Compared with traditional LIBS, the characteristic spectral line intensity and SNR collected by CC-LIBS have been improved, which provides new experimental basis and ideas for the detection of Al and Si elements in bauxite and has certain reference value.