The influence of depth and diameter on spatially confined laser-induced silicon plasma spectroscopy with cylindrical cavity was studied in air. 5×5 groups of cylindrical cavities were used to confine the laser-induced plasmas in current experiments, with diameters of 4, 6, 8, 10, and 12 mm. Each diameter corresponded to five different depths: 2, 4, 6, 8, and 10 mm, respectively. A Q-switched Nd: YAG laser with the repetition of 10 Hz and the pulse width of 10 ns was used to excite plasma inside different cylindrical cavities with various diameters and depths. Laser energy was 70 mJ. In current experimental conditions, when the diameter was 6 mm and the depth of cylindrical cavity is 2 mm, the line intensity of Si (I) 390.55 nm could obtain the maximum. Continue to increase the diameter and depth of cavity, the line intensity of Si (I) 390.55 nm decreased. We hope that this study serves as a helpful reference for future research on spatially confined LIBS.