An Erichsen cupping test of GZ31 sheet at room temperature with different reductions was carried out, and four samples with IEs (Erichsen index) of 2.0, 4.1, 7.1, and 7.3 mm were obtained. The deformation and fracture mechanisms of the cupping deformation process were studied by OM, SEM and EBSD. The results show that the IE of the GZ31 rolled sheet with the non-basal texture can reach 7.3 mm. Basal and pyramidal dislocation slips and {10 2} extension twinning are the main deformation modes during the Erichsen cupping test. The dislocation slip is hindered by the second phase particles and grain boundaries and entangles with each other to form voids, which eventually leads to the fracture of the material. The reason for the GZ31 sheet showing high IE is that the weak non-basal texture and rare earth elements are favorable for dislocation slip and extension twining to coordinate deformation.