By taking soil samples as targets, a small carbon chamber was used to perform the spatial confinement for high energy laser induced plasma to improve the quality of laser-induced breakdown spectroscopy. A high energy laser was used to ablate the soil samples, a spectral analysis system consisting of a modular multifunctional grating spectrometer and a CCD detector was adopted to record the spectral information, and the changes of the radiation intensities of laser-induced soil plasma with and without the small carbon chamber were studied. Then, the electron temperature and electron density of the plasma were measured by the spectroscopic methods to explain the mechanism of irradiation enhancement of the plasma. Experimental results show when the laser plasma is confined by the small carbon chamber , the spectral line intensities of the sample elements Mn, K, Fe and Ti increase about 90.77%, 101.71%, 104.27% and 60.77% than that without the small carbon chamber, and spectral signal-to-noise ratio raises around 54.29%, 55.30%, 59.37% and 38.80%, while the electron temperature and electron density of the plasma enhance about 1 684 K and 1.8×1016 cm-3, respectively. These results demonstrate that the spectral intensities and signal-to-noise ratio of the laser-induced plasma can be improved effectively by spatial confinement for the high energy laser induced plasma, which is an effective means for detecting the low-content elements in soil samples.