Abstract: It is complex to analyze the torsional behavior of steel-box concrete beam because its complex section with the properties of both solid and hollow members. Two different methods for the investigation of the torsional behavior of the beam are thusly suggested by analyzing the characteristics of the pure torsion stress function. The two methods are respectively difference method and simplified method, simplifying the member as a box beam with two cells. The torsion stiffness and shear stress calculated by the difference method are close to their corresponding test results. Besides, numerical analysis shows that if the area occupied by the concrete on the cross-section is less enough, the stiffness calculated by ignoring the concrete can also satisfy the engineering requirement.