The　torsional　effect　of　prestressed　corrugated　steel-concrete　composite　girders　(PCSCCG)　is　more　prominent　due　to　its　low　torsional　stiffness,　which　is　therefore　crucial　to　be　clarified　for　safe　design.　This　paper　proposed　a　theoretical　model　based　on　the　combined　actions　softened-membrane　model　(CA-SMM)　to　predict　the　torsional　response　of　PCSCCG.　The　equilibrium,　compatibility　and　constitutive　equations　were　established　to　consider　the　characteristics　of　corrugated　steel　webs　(CSW)　and　prestressing　effect,　where　a　reasonable　shear　strain　assumption　was　presented　to　determine　the　force　behavior　of　concrete　slabs　and　CSW,　and　the　thickness　of　shear　flow　in　concrete　slabs　was　corrected.　An　optimized　algorithm　using　the　gradient　descent　method　was　established　to　improve　the　insufficiency　and　stability.　Based　on　this,　a　simplified　design　method　was　proposed　to　rapidly　evaluate　the　torque　and　twist　of　PCSCCG.　Finally,　the　feasibility　of　the　proposed　model　and　simplified　design　method　was　verified　by　available　tests.　The　superiority　of　the　analytical　model　in　predicting　the　full　torsional　performance　of　PCSCCG　was　proved,　and　the　reasonability　and　simplicity　of　the　simplified　method　in　capturing　the　cracking,　yield,　and　ultimate　torques　and　twists　were　observed.