To address the contradiction between idle resources in closed coal mines in China and the shortage of empirical research facilities for mine safety, this study proposes an overall concept of constructing an engineering-scale in-situ test site by repurposing closed coal mines. Using Qinneng No. 3 Mine as the engineering background, and based on the “origin–in situ–in-field”concept, a roadway suitability evaluation system was established, comprising five primary indicators including safety controllability and module compatibility. The AHP–entropy weight method was employed to quantitatively optimize and select underground spaces. On this basis, seven categories of in-situ testing platforms—covering mine fire and ventilation, gas, rockburst, roof strata, water hazards, intelligent robots, and rescue drilling rigs—together with a ground-based integrated experimental control center were planned and designed. The total designed roadway length is 6,958 m, of which 6,183 m reutilizes existing roadways, achieving a roadway reuse rate of 88%. The results indicate that the proposed design can overcome the “scale effect” inherent in traditional laboratory research and can effectively enable the low-cost, large-scale construction of realistic disaster-simulation environments, providing a new pathway for the transformational utilization of closed coal mines.