<p>In this study, the accelerated corrosion mechanism of E690 steel in artificial seawater (ASW) with H₂O₂ addition and its effect on the degradation process of mechanical properties were investigated. The results indicated that the addition of H₂O₂ significantly enhanced the accelerated corrosion of E690 steel. This enhancement was achieved primarily through an increase in the dissolved oxygen content in the solution and modifications to the phase composition and structure of the rust layer formed during corrosion. Furthermore, the surface pits generated by accelerated corrosion considerably influenced the degradation process of mechanical properties. When the average pit depth was shallow, the degradation was mainly governed by the uneven distribution of pitting corrosion. As accelerated corrosion progressed and the average pit depth began to affect the effective cross-sectional area, the loss of effective thickness became the dominant factor in the degradation process of mechanical properties.</p>