Abstract: In Longyou Caverns,some of which are full filled with water and keeping their integrity for thousand years,Some others of which are not full filled with water and failures occurred in them. Therefor,an idea can be got from it that full filling with water is a key factor making the caverns keep their integrity for thousand years. In order to verify the idea,the chisel imprints inside and outside of the caverns are measured. Qualitative and quantitative analyses are carried out to study the weathering rate of surrounding rock when it is in different environment under or above water table. The comparison results show that when the cavern is full filled with water all the time,the weathering rate of surrounding rock is relatively slower than that of the caverns not full filled with water.Moreover,numerical computation are carried out to compare the stress distribution of surrounding rock and vertical displacements of the roof. The computaion results verify that full filling with water is benefit for the stability of cavern. When the cavern is full filled with water,the amount of zones in tensile stresses and the tensile stress values of surrounding rock are both smaller than that in the cavern of not full filled with water. When the cavern is part full of water,the improvement of stress distribution is not obvious,the vertical displacements of roof are also increased,which are also not benefit for the stability of the caverns. It can be drawn from above studies that full filling with water is the key factor which makes the caverns keeping their integrity for thousand years.