In order to predict the viscosity of liquid and correlation between equilibrium and the glass state, the theory for composite materials and suspensions was applied to an appropriate composition range of a ternary glass-forming system where one liquid and one crystal are in a state of equilibrium. According to the results the theoretical calculation showed good agreement with the measurement within the validity of the theory. The viscosity behaviour of both results was discussed from the viewpoint of the physicochemical structure of liquid and it was suggested that glass reflects latently some characteristics of the state of equilibrium.