Abstract: There are many folded fissures in the rock masses. In order to explore the fracture mechanism of these rock masses, the sandstone specimens containing a folded fissure are prepared and the uniaxial compression tests are performed. The digital image correlation (DIC) method is used to calculate the evolution of deformation field during the loading process. The crack type is identified by the displacement difference between the initiated crack sides. The extended finite element method (XFEM) is used to simulate the fracture process. According to the stress distribution characteristics, the wing crack initiation and propagation mechanism are explained. The DIC calculation results show that the strain localization bands appear at the locations of the initiated cracks and the relative separation occurs at the two sides of the cracks. For sandstone specimens containing a straight fissure and a folded fissure, the wing cracks initiate at the tips of the pre-existing fissure and at the angle of fissure, respectively. The reason for this is that the location of tensile stress concentration is dominated by the geometric shape of the fissure. The crack initiation stress of the sandstone specimen containing a folded fissure is smaller than that of the specimen containing a straight fissure, because the maximum tensile stress of the former is larger under the same loading condition. The crack propagation of these specimens is caused by the concentrated tensile stress at the crack tip and the propagated cracks remain open. The geometric shape of the fissure does not change the final failure mode of the specimens, which is shown as the diagonal shear failure.