To promote the application of laser-induced breakdown spectroscopy (LIBS) for detecting heavy metals in soil and improve the heavy-metal detection sensitivity, we investigate the enhancement effect of adding different proportions of NaCl powder to soil samples on the LIBS spectrum of Cd. The results show that adding NaCl to soil samples can significantly increase the intensity of the characteristic spectral lines of Cd. When NaCl doping mass fraction is 90%, detection limits of Cd 214.441 nm and Cd 228.802 nm decrease from 30.57 and 28.12 mg/kg to 1.526 and 2.501 mg/kg, respectively. The plasma temperature and electron density are calculated, and the results show that both gradually increase with an increase in the NaCl doping mass fraction. NaCl doping can effectively improve the coupling efficiency of the laser and soil, increase the ablation amount in soil, and thus, enhance the spectral intensity of Cd. The research results are significant for applying LIBS in detecting trace heavy metals.