Abstract：Abstract：There are some damages and separating deformation in the roof of Longyou grotto No.5. According to in-situ investigation and measurement，separating deformation of roof at the grotto exit accumulated to 75–78 mm，and there are damages and fracture phenomenon like cantilever beam at lateral side of grotto roof. In order to understand the fracture process of the roof for grotto No.5 and long-term stability，the numerical simulation and back analysis of rheologic fracture are carried out by using in-situ damage pattern and deformation data，based on the tracking method of maximum tensile stress and the back analysis of rheologic fracture presented by the authors. In the process of back analysis，the orthogonal experiment is used to design 27 kinds of the schemes of numerical simulation. The optimum scheme of parameters which are composed of the rheologic parameters of rock layer，thin double-layer and other sensitive parameters is obtained by analyzing the orthogonal experiment results. The long-term stability and the process of rheologic fracture are analyzed by utilizing the obtained optimum scheme. The calculated results show that the separating deformation of the roof at the grotto exit is 54.24 mm and the fracture location is same as the location of in-situ fracture. In addition，the separation deformation of roof at the grotto recess is also very obvious in rheologic numerical simulation；and the phenomenon is similar to the apparent form of in-situ deformation.
