To　study　the　full　range　performance　of　prestressed　concrete　beams　under　bending-torsion　coupling　effect,　an　improved　theoretical　model　of　full　range　analysis　in　bending-torsion　coupling　effect　was　proposed　based　on　the　combined　action　softening　truss　model　(CA-STM).　Firstly,　according　to　the　bending-torsion　coupling　force　mechanism　of　prestressed　concrete　beams,　the　equilibrium　equations,　compatibility　equations　and　constitutive　relationships　satisfying　the　initial　stress-strain　relationship　caused　by　prestress　were　established.　Then,　the　initial　torque　formulas　of　hollow　and　solid　sections　considering　the　prestressing　effect　were　introduced　based　on　the　previous　codes.　Additional　the　equations,　the　strains　and　compatibility　relations　for　thin　walls　were　established,　and　the　simplified　equivalence　methods　for　steel　and　prestressing　tendons　were　also　proposed.　On　this　basis,　the　gradient　decreasing　method　was　used　instead　of　the　traditional　trial-and-error　method　to　improve　the　solution　rate　and　stability,　and　the　solution　program　for　the　bending-torsion　coupling　analysis　of　prestressed　concrete　beams　was　prepared　by　MATLAB.　Finally,　the　proposed　theoretical　model　was　validated　by　comparing　the　existing　experimental　and　theoretical　results.　It　can　be　concluded　that　the　established　initial　torque　equations　for　hollow　and　solid　sections　are　in　good　agreement　with　the　existing　test　results.　The　result　shows　that　the　cracking　and　ultimate　torque　values　predicted　by　the　improved　model　are　underestimated　without　considering　the　prestressing　effect.　The　improved　model　accurately　predicts　the　full　range　torque-twist　curves　and　bending　moment-curvature　curves　of　prestressed　concrete　members　subjected　to　bending-torsion　effect.　Compared　with　the　traditional　trial-and-error　method,　the　proposed　optimized　algorithm　provides　a　higher　solution　rate　and　stability,　and　its　average　computation　time　is　only　12　s.　3　tabs,　12　figs,　23　refs.　©　2025　Chang＇an　University.　All　rights　reserved.