So far there has been no a ripen criterion to judge the stability of a rockmass that can be accepted unanimously. That is

no a clear system has not been formed yet that covers a series of basic problems

such as definition and quantitative judgment of stability or theory and method and criterion to analyze rockmass stability. At present

the commonly used method it to judge the stability of rocks surrounding a project according to plastic zones. However

this method is just used mainly for determining the failure scope of surrounding rocks. It is too dangerous if the method is used to determine the minimum rock cover thickness above a submarine tunnel

because ordinary submarine tunnels are mostly excavated in hard rocks

producing small plastic zones. Therefore

it is necessary to establish a method to determine the minimum rock cover thickness of a submarine tunnel. The mumerical analysis method FLAC3D applicable to simulalating large deformations of rocks and soils is adopted in this paper to establish a criterion according to the deformation or deformation rate criterion of surrounding rocks that be used for determining the minimum rock cover thickness of a submarine tunnel. This criterion has been successfully used in Xiangshan harbor’s submarine tunnel

and the estimated minimum rock cover thickness is coincident with that from traditional engineering analogy method

which shows the rightness and avidity of the method proposed in the paper.