A system and a method of measuring irregularity of a glass substrate using only a reflection light reflected by an upper surface of reflection lights reflected by the upper surface and a lower surface of the glass substrate are disclosed. The system includes a light source section configured to output a first light to the glass substrate and a screen. Here, the first light outputted from the light source section is reflected by an upper surface and a lower surface of the glass substrate, a first reflection light reflected by the upper surface of the glass substrate is inputted into the screen, a first line is formed on the screen in accordance with the input of the first reflection light, a second reflection light reflected by the lower surface of the glass substrate is inputted into the screen through the upper surface, a second line is formed on the screen in accordance with the input of the second reflection light, and the light source section and the screen are disposed on the basis of the glass substrate so that the lines are separated.