Abstract: In order to test the stability of rock formations in underground mined-out areas under a city,a three-dimen- sional geomechanical modeling was carried out to test the potential destruction of the potential geo-logical hazards in a city. According to the similar simulation theory,a similar material was configured with medi-um-rough river sand as ag- gregate,and a similar model was established using the masonry method. The rock strata was gradually loaded until the model damage,and the surface displacements,changes in the strain of the pillars and the roof of the rock were moni- tored,and the destruction and evolution of the roof and pillars were photographed by endoscopes. The relationship be- tween the displacement of the rock surface,the curvature deformation,the strain in the roof and pillars,and the in- creasingly load were calculated. The stability of the rock formation was comprehensive analyzed in several aspects. Ac- cording to the test results,when the rock surface load is less than 2 MPa,the rock surface deformation is very small, and the deformation rapidly increases after 2 MPa,and it shows obvious non-uniform deformation characteristics. When the rock surface load does not exceed 1. 2 MPa,the roof strain is in a small linear deformation stage. When the local surface load increases to 5 MPa,a sharp inflection point appears on the strain curve,and the roof plate begins to fail. According to the image records,the roof plate was damaged by tensile cracks before the pillars,and pillars appeared cracking. Therefore,the future failure mode will definitely be that the roof is damaged before the cracks occur in pil- lars. Therefore,the stability of the rock formation could be controlled by preventing the roof from cracking. In summa- ry,the transient load on the surface of the rock formation is finally determined to be 1. 2 MPa. In future development and design,the problem of uneven deformation caused by the existence of underground irregular goaf in rock forma- tions in this area should be fully considered.