Abstract: For the sake of security during the process of excavating an underground grotto， the early safety warning indexes of the underground grotto are defined in advance and treatments are made as soon as possible, which is a key to ensure the stability of the surrounding rock. A numerical model is created based on the geological data， and the displacement curves of different sections can be obtained by FEM. With some technical codes of maximum displacement of the surrounding rock， the early safety warning indexes of the underground grotto can be confirmed by the displacement which can be measured easily. At last， a circular underground grotto is created using four different groups of geological data， and the early safety warning indexes of the underground grotto are solved by this method. Compared with the plastic zones of the surrounding rock， the early safety warning indexes which can be defined by the numerical method and some technical codes can be used to judge whether the underground grotto can be saved or not. The method of the early safety warning indexes of the underground grotto is feasible.