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Ge2Sb2Te5 (GST) is a technologically important phase-change material for data storage, where the fast reversible phase transition between crystalline and amorphous states is used for recording information. The effects of vacancies on crystal GST were investigated by ab initio calculations. Based on analysis of the vacancy formation energy, the GST structure with Ge vacancy (VGe) was found to be the most stable. Thereafter, the influence of VGe defects on crystal GST structure was deliberated by analyzing the band structure, electron density difference, total density of states (TDOS) and partial density of states (PDOS) of GST structure. The results reveal that VGe can promote the Fermi level enter into the valence band, which makes the GST material exhibit more pronounced properties of P-type semiconductors. Nevertheless, VGe shows a slight effect on the chemical bond characters. When VGe concentration maintained at 20% in the GST structure, the band gap is the widest about 0.45eV. Moreover, VGe can result in the electrons in s orbital of Ge, Sb and p, d orbitals of Te make a contribution to the valence band, while electrons in p and d orbitals of Ge, Sb are more favorable to conduction band.

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