Studying the asymmetric spatial effects of LIBS is crucial for enhancing defect spectral detection accuracy in metal additive manufacturing (AM). A parallel wall cavity was used to simulate asymmetric conditions of crack defects, with the distance between the ablation point and the left wall (DAPLW) systematically varied. Experimental conditions were established for both symmetric (DAPLW = 7 mm) and asymmetric (DAPLW = 1-6 mm) configurations to study the spatiotemporal distribution of plasma under different spatial effects. Results revealed that asymmetric spatial effects significantly influenced the spatiotemporal distribution of plasma, causing more complex fluctuations in spectral intensity and changes in plasma morphology. Under asymmetric spatial effects, plasma showed enhanced spectral intensity at various acquisition delay times (e.g., 7 μs and 13 μs at DAPLW = 4 mm). However, spectral intensity fluctuations also increased, indicated by a higher relative standard deviation (RSD). Additionally, the study examined the impact of various point-wall distance constraints on the plasma’s time evolution and observed a significant shift in the core position of plasma (CPP) (10-22 μs). During this process, the near roundness ratio of plasma (NRRP) value exhibited significant changes (10-13 μs), particularly when the DAPLW was 1 mm. It decreased from a stable value of 0.8 to below 0.1, reflecting notable morphological changes. In contrast, the symmetric space effect and unconstrained plasma behavior remained stable, with spectral intensity changes showing clear regularity and only relatively small alterations in plasma morphology. This indicated that the delay time of the acquisition system is crucial for using LIBS technology to detect defects in metal AM components with asymmetric cavities. Therefore, understanding asymmetric cavity effects enhances plasma behavior knowledge and provides new guidance for improving defect detection accuracy.