<p>Deep-sea pressure vessel operates in extreme marine environments characterized by high pressure, low temperature, and high corrosion. These conditions impose stringent material requirements, especially for high-strength steels used in deep-sea pressure vessel hulls. In addition to high strength, these steels must exhibit excellent low-temperature toughness, seawater corrosion resistance, weldability, and high-cycle fatigue life. However, achieving an optimal balance between strength and toughness remains a core challenge in developing high-strength steels for practical applications. Therefore, this review focuses on high-strength steels used in deep-sea pressure vessel hulls, specifically high-strength low-alloy steels, Co–Ni secondary hardening steels, and maraging steels. The strengthening and toughening mechanisms of these steels in terms of alloy elements, heat treatment, and microstructure control were analyzed. The review indicates that high strength is primarily achieved by reinforcing martensitic matrix with high-density dislocations, nanoprecipitates, intermetallic compounds, and Cu-rich particles. High toughness is attained by refining the martensitic microstructure, controlling the stability of metastable austenite, and introducing low lattice misfit nanoprecipitates. Based on these findings, we propose a novel design concept: the synergistic co-precipitation of low lattice misfit nanoprecipitates and reversed austenite within high-density dislocation martensitic matrix to achieve an optimal balance of strength and toughness. As digital steel and advanced heat treatment technologies mature, this concept is expected to provide strong theoretical support for the development of high-strength steels used in deep-sea pressure vessel hulls.</p>