Abstract: A beam string structure is formed by tensioning the prestressed high strength cable in the low part of a solid web steel beam or a steel truss. However, the prestress of the cable is sensitive to temperature change. Therefore, fire is an important disaster for the safety of a beam string structure. The analytical calculations of mechanics characteristics are a theoretical basis to further study the fire safety performance. Considering the geometric distortion with thermal stress coupling temperature distribution and the non-linear temperature-dependent material properties for a steel beam and its cable, the equilibrium differential equations of the beam and cable at high temperature are established, and formulas are developed for the calculation of mid-span deflections, the horizontal tension in the cable, and axial forces of the struts subjected to fire under linear load. Additionally based on the analytical calculations of mechanics characteristics, the reliability of the nonlinear numerical model for the fire safety performance of a beam string structure is compared. This study can provide a reference for subsequent fire -resistance tests and studying the failure mechanism of beam string structures subjected to fire.