Abstract: Using the techniques of geomechanical mechanism simulation of resemble material,the tectonic gravity spreading mechanism of Xian ground fissures is reproduced and testified in this paper.Some important conclusions,such as the tectonic gravity spreading mechanism is the essential reason for the ground fissures,the engineering buildings can be safely planned if only keeping a certain distance from the ground fissures,the maximum depth of the around fissures extend is likely at the upper-middle part of Paleogene deposits,etc. are drawn out. The reason for the abnormal land subsidence is revealed preliminarily. The results has obvious theoretical significance and social-economic benefit.