The crystalline morphology and the phase evolution of Mg-6Zn-Y alloy solidified under a super-high pressure were investigated by scanning electronic microscopy (SEM) coupled with the energy disperse spectrum (EDS) and the X-ray energy diffraction (XRD). The results show that with the increase of solidification pressure, the crystalline morphology transition from a coarse equiaxed dendritic to a super-fine equiaxed dendritic, to a columnar dendritic, and to a granular “cellular” is observed in the microstructure, suggesting the solid/liquid interface is stable. The microstructure of the alloy solidified under 10-9 GPa consists of three phases, i.e. α-Mg phase, I-Mg3Zn6Y phases and S-Mg43Zn4Y3 phase, while the microstructure of the alloy solidified under 2~6 GPa consists of four phases, i.e. α-Mg phase, I-Mg3Zn6Y phase, S-Mg43Zn4Y3 phase, and ternary Mg-Zn-Y phase with high Y content