<p>The recently developed SCCDS composite tube, a novel variant of the pipe-in-pipe (PIP) structure, demonstrates strong potential for subsea pipeline applications. However, theoretical research regarding its structural behavior under compression-torsion loading and bearing capacity calculations remains limited, particularly concerning the influence of dual hydraulic pressures during operation. This study examines the impact of dual hydraulic pressures on the compressive-torsional behavior of SCCDS composite tubes. A finite element (FE) model was developed and validated against experimental results, comparing failure modes, full-range loading curves, and bearing capacity to elucidate the working mechanism under dual pressures. A parametric study was then conducted to examine the effects of geometric-physical parameters. Results demonstrate that dual pressures substantially enhance the bearing capacity of sandwich concrete by increasing the normal contact stress at the interface. Increasing concrete strength (<i>ƒ</i>_c) provides minimal enhancement to torsional resistance compared to the yielding strengths of outer tube (<i>ƒ</i>_yo) and inner tube (<i>ƒ</i>_yi). Higher diameter-to-thickness ratios of outer tube (<i>D</i>_o/<i>t</i>_o) and inner tube (<i>D</i>_i/<i>t</i>_i) significantly reduce torsional capacity. At 1000 m water depth, increasing the <i>D</i>_o/<i>t</i>_o ratio from 27.5 to 36.67, 55, and 110 reduces bearing capacity by 11.17%, 23.08%, and 36.14% respectively. Strict measures should be implemented to prevent substantial reductions in strength and ductility for SCCDS composite tubes with large hollow ratios (e.g., <i>gC</i>=0.849) or high axial compression ratios (e.g., <i>n</i>=0.8). The study proposes a modified calculation method for determining <i>N</i>-<i>T</i> curves that incorporates dual hydraulic pressure effects, providing guidance for performance evaluation of novel SCCDS composite tubes in deep-sea engineering.</p>