Changes in the basement tends to cause the overburden to rupture and deformation and damage to structures such as surface structures,underground pipelines,and tunnels. In order to explore the development process and mechanism of basement extensional ground fissures,this paper reveals the variation law of deformation and displacement of overlying soil caused by basement extension through physical simulation experiments,and analyses the section structure characteristics of fissures and the development and fracture process. The results show that under the tensile stress of the substrate,the overlying soil on the fault will be"pushed"to release stress. With the continuation of horizontal tension,the settlement and thinning of overlying soils occur first,and especially,the response of soils with strong plasticity is more obvious. Under the action of continuous stress,cracks extend from bottom to top until they penetrate the surface. In addition,the closer to the ground fissure,the larger the amount of sedimentation and thinning of the soil is,and the smaller the density becomes.