Abstract: To enhance the spectral signal intensity and stability of laser-induced breakdown spectroscopy (LIBS) for detecting trace elements in soil, a graphene oxide (GO) adsorption conversion mechanism is proposed. The experiment compared the enhancement effects of three substrates—glass plate, graphite plate, and GO adsorption layer—on metal elements such as Ni, Sr, and Ba in soil. The surface enhancement mechanisms of different substrates were analyzed from three perspectives: ablation morphology, thermal conductivity, and adsorption energy. It was concluded that a smooth substrate surface facilitates uniform solute distribution, and an increase in the thermal conductivity of the substrate material enhances the signal and enlarges the plasma morphology. The optimal soil-to-nitric acid ratio in the solid-liquid-solid conversion mechanism was determined to be 1:1, with a nitric acid concentration of 1 mol/L. The GO adsorption layer substrate demonstrated the best enhancement effect, with spectral intensities of Ni, Sr, and Ba enhanced by 3.4, 1.8, and 8.3 times, respectively, compared to the glass. The limits of detection (LOD) reached 3.148 mg/L, 0.578 mg/L, and 0.322 mg/L, with relative standard deviations (RSDs) of 5.4%, 6.8%, and 8.5%, respectively. This indicates that the solid-liquid-solid conversion mechanism using the GO adsorption layer can effectively enrich metal elements in soil, enhancing the spectral signal and stability of LIBS in detecting trace elements while significantly lowering the detection limits. This approach provides a new strategy for the accurate measurement of trace elements in soil samples using LIBS.