Abstract: Operational shield tunnels are often affected by nearby surface loads, excavation of foundation pits, and piling activities. The external complex loads acting on the shield tunnel can disrupt the original force balance of the structure, potentially leading to excessive deformation or damage. Conducting full-scale tests is the most direct and effective means of studying the mechanical performance and failure characteristics of tunnel structures under complex loads to accurately assess the applicability of tunnel structures. To expand the applicability of full-scale tests for shield tunnels, a prefabricated steel reaction frame suitable for full-scale tests of shield tunnel structures with different sections has been proposed. The horizontal applicability of the reaction frame for different sections and sizes of structural tests is achieved through the combination of different standard units and flange-type node connections. In the vertical direction, nested column connections are adopted to effectively solve the connection and shear transfer between layers of the reaction frame. Meanwhile, the overall stress and node strength of the reaction frame were checked against four extreme loading conditions, and the feasibility of this prefabricated loading platform was further verified through the prototype structure loading test of a circular shield tunnel.