The morphology of sandstone fracture main crack and subcritical fracture crack (that growth due to stress concentration but not turn into fracture main crack) in mesoscale level have been systematically investigated through the three-point bending fracture test with scanning electron microscope (SEM). It is shown that the fracture of sandstone behaved complicatedly

and correlated with not only the composition of sandstone binding material but also the distribution of sandstone fragmentary particle. Furthermore

there give birth to many subcritical fracture cracks in the fracture process. The morphology of fracture main crack and subcritical fracture crack is similar. Ductile fracture has been taken place if the specimen has many subcritical fracture cracks in the fracture process zone. Contrary that brittle fracture will be taken place.