Abstract: With prescribed generalized coordinate, the differential equation system for restrained torsion analysis of composite beams is established based on the principle of generalized coordinate method. An extension spring and a slipping spring are introduced to simulate the effect of detachment and slippage on the interface between concrete slab and I-shaped steel beam. The solver of ordinary differential equations (ODEs)--COLSYS is employed to solve the system equations. A practical example is studied to demonstrate the method.