Abstract: Similarity simulation experiments offer a direct and visual method for reproducing the formation and evolution process of fire and gas compound disasters in a goaf. However, existing experimental platforms suffer from issues such as the lack of a theoretical basis for determining similarity ratios, small geometric dimensions, and overly simplistic system structures, making it difficult to realistically replicate the complex environmental characteristics of an underground goaf. To address this issue, the design principles for a physical similarity model of a stope were introduced. Based on the equations for mass, momentum, and energy conservation, as well as the concentration equation within the goaf, similarity theory was applied to derive and quantify the proportional relationships among the physical parameters of the experimental platform. A similarity experimental system for fire and gas compound disasters in a goaf was designed. The system was primarily composed of the following core units: a physical similarity model of the stope, which served as the foundational platform; a coal spontaneous combustion simulation unit to simulate the process of coal spontaneous combustion; a flammable gas simulation unit to establish the gaseous environment in the goaf; a real-time gas information acquisition and analysis unit to analyze changes in gas information within the physical model; and an inversion analysis unit for the fire and gas compound disaster, which performed the full-process simulation and inversion analysis of the coupled disaster chain of coal spontaneous combustion, gas accumulation, and explosion in the goaf. The results of the comparative analysis revealed that the system was capable of achieving a flexible configuration of the experimental environment while ensuring geometric similarity. The proposed system demonstrates significant advantages over existing systems with respect to simulation function, similarity, parameter control, operational convenience, and the reliability of experimental results.