Abstract: To address the limitations of conventional geophysical methods in detecting concealed voids in complex underground environments, including limited resistance to environmental interference and insufficient spatial resolution, this study systematically investigates the application of cosmic-ray muon imaging technology. The characteristics of the muon source, imaging theory, and forward and inverse modeling methods are described in detail. The feasibility of detecting concealed voids above tunnels is further evaluated. The results show that, for a tunnel depth of 25 m, voids with dimensions of 2~3 m can be effectively identified using a 3 h observation period. When the tunnel depth increases to 100 m, the minimum detectable void size increases to 5~6 m under continuous observation for 24 h. These results demonstrate a nonlinear degradation of detection capability with increasing depth, primarily attributed to the rapid attenuation of muon flux.