A selenization process apparatus for a glass substrate includes a first heating unit disposed in a chamber; a conveying heating module disposed in the chamber and below the first heating unit to not only drive the glass substrate to move but also heat the glass substrate, wherein a thermal mark otherwise formed as a result of contact between the conveying heating module and the glass substrate is reduced with an inert gas; a selenium gas feeding module connected to the chamber to introduce selenium gas into the chamber; and a gas recycling module connected to the chamber to recycle the selenium gas and the inert gas. The glass substrate is prevented from staying at a soaking temperature above the softening point for a long period of time. Selenization temperature is increased to speed up the selenization process. The selenium gas and the inert gas are recycled and reused.