Abstract: The in-situ stress is obviously important to the stability of the underground opening in brittle hard rock.Previous researches generally focused on the brittle failure fashion and its prediction,the relation of the in-situ stress and the depth of brittle failure is extremely insufficient.In the paper,based on the brittle failure criterion,the relationship between the different in-situ stress environment,opening shape and the depth of brittle failure d_f have been analyzed by Examine2D software.Conclusions can be drawn as follows:with the increase of principal stress ratio k value,d_f shows increase trend in the form of line in the low minimum principal in-situ stress,in the form of non-line in the high minimum principal in-situ stress and damaged region diverge the direction of the minimum principal stress to the angle of 45° between the minimum in-situ stress.The influence of the direction of principal stress is lower than the value of the principal stress when tunnel's length similar to width.The site of brittle failure is different with different tunnel shape in the identical in-situ principal stress environment,but the depth of brittle failure is minor.Stress concentration factor in different excavation shape is different.The depth of brittle failure effectively reduced when the prolate axis vs minor axis equal to the k in ellipse cavern.