The computational modelling of the over-flow fusion process, manufacturing a flat glass for the use of TFT-LCD, was carried out. The flow rate and the viscosity of molten glass flow, influencing the formation of a flat glass, as they encounter to the geometry of an apparatus, was studied. Using an analogy method, a physical experiment of molten glass flow was conducted. The result of computational modelling was validated by the experiment. In modelling, a general CFD code (Flow3D(superscript TM) was used. In the numerical model, the continuity and momentum equations were incorporated with the free surface transport equation. In the result of modelling the overflow process, the thickness of the formation of a sheet glass was influenced by the geometry of overflow trough, and the flow rate and viscosity of molten glass flow.