Abstract: The reasonableness and limitations of the failure criterion for rock in terms of stress are described and it is emphasized that development of failure criterion in terms of strain has been of great significance on rock engineering design.According to the test data on rock specimen, critical strain curves are presented as rock failure criterion.. Finally, the general approach of direct strain analysis to the stability of underground excavation is introduced. Obviously, combination of the two kinds of rock failure criterion would be one of the significant characteristics on rock strength theories.