Abstract: Amid the concurrent pressures of energy transitions and marine ecological risks, polymetallic nodules, polymetallic sulfides, and cobalt-rich crusts are increasingly recognized as potential sources of strategic mineral resources. Their environmental governance has thus become a focal point in both international and national policymaking. To address the limitations of existing studies, which often remain confined to single-mechanism reviews or fragmented policy descriptions and lack a systematic comparative framework, this study first develops a three-level analytical framework—comprising principles, rules, and technology—to deconstruct the international governance architecture centered on UNCLOS and ISA, and supported by UNEP, IMO, and ISO. This framework clarifies the internal logic and functional boundaries of the current regime. Secondly, to elucidate the evolution of national governance models, it establishes a six-dimensional framework covering strategic orientation, legal and permitting regulations, administrative responsibility, international contract engagement, scientific monitoring support, and transparency and public participation mechanisms. Using resource development impetus and ex ante risk constraints as classification criteria, it groups nine representative countries into three policy pathways: proactive advancement, cautious piloting, and precautionary pause. The findings indicate that, at the international level, multilateral coupling improves regulatory operability, yet institutional uncertainties persist regarding threshold enforceability and cross-regime coordination. Although national approaches diverge markedly in access thresholds and implementation pace, they converge on a shared governance logic that integrates ex ante environmental impact assessment, process monitoring and information disclosure, and ex post adaptive correction and institutional adjustment. Based on these international comparisons, it recommends that China refines its mandatory technical standards, enhances EIA transparency, improves alignment between environmental liability and compensation regimes, and strengthens long-term baseline surveys and continuous monitoring capacity.