Abstract: Low horizontal ground stress is a stress state which is always neglected in underground engineering.It has important influences on the stability of underground engineering.By analyzing the ground stress influencing characteristics,it is pointed out that the ground stress analysis should begin with an analysis of geological formation and structure features.Due to different problems existing in the ground stress measurement,geological mark judgment methods of low horizontal ground stress in underground engineering are provided in this paper. With a combination of the low horizontal ground stress conditions,the classification methods of discontinuity strength of block combinations are also suggested,and a common 2-D block calculation relation is deduced.A practicable application is carried out with reasonable results.