Excessive self-weight and difficulty in construction are the main issues confronted by super-long-span arch bridges. To address these issues, a conceptual design of steel-ultra-high performance fibre-reinforced concrete (UHPFRC) composite truss arch bridge with a main span of 1000 m was proposed, and the corresponding structural responses were numerically investigated based on finite element analysis (FEA) in this study. In this proposal, the UHPFRC was applied to box arch ribs for bearing the large axial forces, and the steel was used for web members and transversal connectors to avoid the risk of cracking. Such composite arch bridge has a much lower self-weight than traditional concrete arch bridges and avoids the need for welding on thick steel plates since only thin steel elements (thickness not exceeding 40 mm) are used compared to steel arch bridges. The cantilever erection with cables support was adopted during the main arch erection. In this scope, the temporary erection cables merely need to bear the self-weight of two truss arches and the transversal connectors during each closure and the process is repeated four times, which thus reduces largely the cost of temporary supports for construction and increases the feasibility of the construction. Based on the FEA results, the UHPFRC arch ribs are always in compression at a maximum compressive stress of 63.8 MPa. Furthermore, the stability, stress, and stiffness of each component during each construction stage meet the requirements of the code. By the comparative studies of the steel arch bridges, UHPFRC arch bridges, and the proposed one, the steel-UHPFRC composite truss arch bridge has significant technical and economical advantages and is suitable for a bridge with a main span in the range of 500 similar to 1000 m.