The influence of geometric characteristics (size and shape) of a pore on phase equilibria in stratifying polymer solutions within porous matrices have been simulated by means of equilibrium chemical thermodynamics. Using the example of liquid stratifying polybutadiene-polystyrene mixtures, we have shown that a strain of a matrix which influences on pore shapes, determines mutual solubilities of components within a pore, equilibrium volume ratios of co-existing phases and their thermodynamic stability. High strains of a matrix lead to suppressing the stratification while every composition up to the equimolar one becomes thermodynamically stable.