This paper presents a new analytical model for nonlinear analysis for flanged RC beams with large web opening subjected to pure torsion to calculate torque and angle of rotation at all stages of loading. The analytical method employs the combination of two different theoretical models: (1) model of concrete softening and (2) space truss model. The softened truss model has been successively used for torsion, which is extended to flanged RC beams with large web opening under pure torsion. The theory of softened truss includes effective transverse compressive stress acting on the torsional element and softened concrete stress-strain relationship for the concrete behavior. The verification of the proposed analytical model is achieved through extensive comparisons between torque-rotation curves that are obtained from current analytical model and experimental ones.