<p>The carcass layer is the innermost structure of flexible marine risers and is responsible for resisting external pressure. It has an “S” section with a spiral interlocking feature. After the multi-pass roll forming of a flat steel strip, a carcass layer is formed by lock forming. During roll forming, the steel strip undergoes significant plastic deformation, and its local area accumulates residual stress owing to multiple loading and unloading cycles. These phenomena complicate the design and analysis of the carcass layer multi-pass roll forming (CLMRF) process and cause issues in the carcass layer during manufacturing, such as strip fracture and low forming quality. Thus, herein, CLMRF was investigated to clarify the stress distribution, and a parameter analysis was performed. First, the CLMRF process was designed on the basis of classical roll-forming design theory. Second, a finite element model was established, and CLMRF was simulated. Third, the distributions of the forming stress and residual stress of the strip during CLMRF were investigated. Finally, the influences of the strip thickness, roll gap, roll distance, and angular increment were investigated. The conclusions of this study can be used to provide technical guidance in the manufacturing of flexible risers.</p>