Brittle constitutive model and slippage destruction theory were used to analyze the stress distribution and failure mechanism of surrounding rock for deep underground project. The result shows that: Excavation unloading will cause the growth of the shear stress

which leading to the local irreversible (plastic) slip or break; and the surrounding rock will be divided into blocks with certain scale; the frictions between the blocks decide the value of the rest strength. Under the action of uneven compression

it can produce zonal tensile breakage

that made the monitored displacement greatly exceed the calculated value with continuum theory. By considering volume expansion

we can get the conditions that cause the tensile breakage; the calculation shows they are related to the material properties and the brocken scale.