Understanding the detection mechanism of hole defects in metal additive manufacturing (AM) components is of great significance for the detection of metal AM component defects using laser-induced breakdown spectroscopy (LIBS). In this work, the mapping relationship between the hole defects of metal AM components and the LIBS spectral signal was studied using the controlled variable method. The effect of hole defects mostly showed a suppression effect and peaked at a hole depth of 1.0 mm when the LIBS system was at its optimal excitation parameter. To explore the possible reasons behind the inhibitory effect of self-holes, the variation law of the plasma temperature with and without hole defects was further investigated. Our results showed that the plasma temperature change curve was similar to the spectral line intensity change trend. Finally, the linear relationship between the focal length effect and the hole effect, and the relationship between the constraint effect and the hole effect were studied. The minimum fitting R2 between the constraint effect and the hole effect was 0.979. We believed that the inhibition of the hole effect was mainly caused by the absorption and loss of energy in the plasma during the process of plasma radiation and shock wave reflection from the hole wall. By studying the detection mechanism of hole defects in metal additive manufacturing components excited by LIBS and finding the effective characteristics of hole defects in metal AM components, it is helpful to achieve higher precision and higher sensitivity defect detection.