Abstract: The assumption of molecules group of glass network was made, and the relation of immiscibility boundary was derived and established. The immiscibility boundary curve of some glass system was
calculated and estimated by using the new theory relation, and the results are closely agreed with the experimental immiscibility boundaries. This relation first solved the non-symmetry curve of immiscibility
for the binary oxides glass system theoretically. It can be considered that this new theory and the equation can be applied in the more glass phase separation systems, and mutual interaction between
different molecules can be calculated further.

Key words: immiscibility boundary, prediction, binary system, oxide glass