Abstract: Longyou Caverns,excavated in politic siltstone near ground surface,are with large span,little support area and long-term stability. According to the modern rock mechanics,the caverns can not keep their stability for thousand years,which evokes more and more attentions from many researchers. The aim of the paper is to reveal the mechanism of the long-stability of the caverns. The caverns are all with inclined roofs trending north. The side-walls,especially the east and west-sidewall both incline to inside of the cavern rather than the vertical ones. The rock pillars are all with iron-shape cross sections. Moreover, there is an arcual support upper part of each rock pil-lar. Are the special structures as mentioned above done by chance or designed elaborately? Is the special structure the governing factor making the cavern be integrity for thousand years? The aim of this paper is to answer these questions by numerical computations,which will reveal the mechanism of the long-term stability of Longyou Cav-erns. The numerical analysis results show that the design of inclined roof can solve the problem of shallow-bury,the iron-shaped rock pillar and the upper part arcual support benefit for the stability of the cavern. The design of in-dined sidewall is favorable to the stresses distribution of the surrounding rock. Then,the conclusion can be drawn from the above study that the special structure is the governing factor making the caverns is in their integrities for long-term stability.