<p>The mechanical properties of corroded reinforced concrete (RC) beams after exposure to fire serve as one of the critical bases for post-disaster structural restoration. To evaluate the bending performance of corroded RC beams after fire exposure, a calculation program was devised. This program was based on section theory analysis and aimed to analyze the mechanical properties throughout the bending process of corroded RC beams. The section theory analysis method specifically accounts for the strain incompatibility between corroded steel bars and concrete caused by bond-slip. Firstly, a compatibility coefficient and finite element model were introduced to quantify the incompatible strain. The effect of corrosion degree and fire exposure time on the coefficient was investigated in detail. Subsequently, a sectional analysis of corroded RC beams was conducted. The entire bending process was divided into two stages based on the concrete stress of the tension zone: before and after cracking. According to the stress state of the steel, the failure mode of corroded RC beams was divided into brittle and ductile failure. The theoretical analysis process was then programmed using Python. The results showed that the error between the program’s calculation and experimental values of the program was less than 5.62%. Finally, the influence of corrosion ratio, thickness of concrete cover, and fire exposure time on the residual flexural capacity and flexural stiffness was discussed. And simplified formulas for each were established. The calculation values obtained from this simplified calculation method are within a 10% error compared to the experimental values. This research can provide a theoretical basis for the reinforcement and repair of corroded RC beams after fire exposure.</p> Graphical Abstract <p></p>