The pressure-induced insulator-metal transition in amorphous GeSe2 (a-GeSe2) is studied using an ab initio constant pressure molecular-dynamic simulation. a-GeSe2 transforms gradually to an amorphous metallic state under the application of pressure. The transition is reversible, and is associated with a gradual change from fourfold to sixfold Ge coordination, and from twofold to fourfold Se coordination. Pressure reduces the occurrence of chemical disorder up to 13 GPa. It is found that the optical gap decreases gradually, and the highly localized electronic and vibrational states of the glass at zero-pressure become extended with an increase of the pressure.