This study investigates the ultimate span of a concrete-filled steel tube (CFST) arch bridge, focusing on structural strength, stiffness, and stability. The finite element method is used to analyze the influence of parameters such as pipe diameter, wall thickness, and cross-section height on the ultimate span. The results show that the ultimate span increases with the pipe diameter and cross-section height initially, then decreases. It also increases with the wall thickness of the steel pipe. The optimal parameters for the ultimate span are determined to be a pipe diameter of 1.49 m, a wall thickness of 37 mm, and a cross-section height of 17 m, resulting in an ultimate span of 821 m, which exceeds the current largest CFST arch bridge in the world. The response surface method is employed to establish a mathematical model for the ultimate span, significantly improving the efficiency of the determination process. Finite element verification confirms the correctness of the optimization results, showing that the structure meets all the limiting conditions.This study investigates the ultimate span of a concrete-filled steel tube (CFST) arch bridge, focusing on structural strength, stiffness, and stability. The finite element method is used to analyze the influence of parameters such as pipe diameter, wall thickness, and cross-section height on the ultimate span. The results show that the ultimate span increases with the pipe diameter and cross-section height initially, then decreases. It also increases with the wall thickness of the steel pipe. The optimal parameters for the ultimate span are determined to be a pipe diameter of 1.49 m, a wall thickness of 37 mm, and a cross-section height of 17 m, resulting in an ultimate span of 821 m, which exceeds the current largest CFST arch bridge in the world. The response surface method is employed to establish a mathematical model for the ultimate span, significantly improving the efficiency of the determination process. Finite element verification confirms the correctness of the optimization results, showing that the structure meets all the limiting conditions.