Recently there is not enough land surface because of increase of use of national land by constructing variety structures. For this reason, design and construction technique of underground space are developing and use of underground space is increasing. Use patterns include tunnel, power plane in underground cavity, underground storage of dangerous things, underground storage of energy resources besides, underground mining are increasing. These kind of things must be careful on the stability because underground structure is constructed in under the ground unlike general structures. This paper was carried out to assess the safety of the underground space by using critical strain in the ground. Sakurai(1982,1997) suggested critical stain what is a new material property of the ground. To predict critical strain applied field data through the design-parameter of ground and field Test. The Methods are numerical analysis by using FLAC 3D and artificial neural networks by using GUI program of MATLAB. Furthermore, predicted critical strain is utilized to assess the safety of underground space using direct strain estimation method. So, this paper suggest reasonable method for predict critical strain.