Glass of MgO-CaO-Al 2 O 3 -SiO 2 system is one of the most focused research and development topics, such as for its wide applications of glass fiber reinforced compositions. The system potentially offers high mechanical properties, especially high fiber tensile modulus for ultralong wind turbine blades. However, challenges remain in processing technology because of its inherent high liquidus temperature. This study provided new insight into using Li 2 O for improvement of fiber glass processing, lower melting/forming and lower liquidus temperature, plus added new benefit, i.e., increasing fiber modulus. The dual functionality of Li 2 O in the glass was detailed in conjunction with Raman spectroscopic study aided by the curve deconvolution analysis, focusing on its influence on the speciation of glass structural groups in comparison with Na2O. Main findings from a separate study of MD simulations were also discussed to gain further insight of Li 2 O roles in the glass network; for the first time, Li-induced higher coordination of aluminum-oxygen structures was revealed, which play a key factor in improving glass modulus.