The present invention relates to a glass substrate composition comprising SiO2 55˜70 wt %, Al2O3 0˜1 wt %, ZrO2 0.1˜5 wt %, Na2O 0.1˜5 wt %, K2O 7˜13 wt %, MgO 7˜14 wt %, CaO 0˜4 wt %, SrO 7˜12 wt % and SO3 0.01˜0.5 wt %. The glass substrate prepared by using the above composition shows less thermal deformation at a baking process under a high temperature since the strain point of the glass is at least 570° C., does not have such disadvantages as increase of fuel cost and short life cycle of refractories resulted from less than 1460° C. of melting point, and has 80˜95×10−7/° C. of thermal expansion coefficient in the temperature range of 50˜350° C. Therefore, the glass according to the present invention is suitable as a substrate.