Chalcogenide glasses of GexSe100-x (x=10, 15, 20, 25 and 30 at.%) glasses were prepared by vacuum melting. An empirical relation between the glass transition temperature (Tg) and is proposed by applying the Gibbs-Di Marzio equation for the Tg of a crosslinked polymer as a function of cross-linked density. We found a good agreement with the experimental result of Tg for GexSe100-x glasses. Several parameters such as mean atomic volume density, compactness, and free volume percentage which are more sensitive to the structure network changes were calculated. Their variation is discussed in connection with the proposed structural model. The variation of the molar volume and Tg with indicates the coexistence of topological and chemical ordering effects. With the structural modification, the number of lone-pair decreases, and the covalent coupling of the structural network increases with increasing Ge content, due to the increases in the crosslinked between Ge and Se bridge.