A new calculation method for the closed-loop coexistence curves of liquidliquid equilibria, the type VI, was developed in terms of the lattice decoration and the UNIQUAC equation by performing two-step renormalization calculation for the molecular orientational interactions and chain dimensional flexibility. In formulating the calculation model consisting of primary and secondary cells, the orientation effect of ghost molecules in the secondary cells was considered together with the molecular geometric information, and the local composition concept of the UNIQUAC model in the primary cells. Two-step renormalization, evaluating the effective interaction energies of sites in the decorated lattice, was performed to obtain the interaction contribution in the activities of mixtures. Directionalities of the orientational site on molecules were assumed to be proportional to the molecular surface areas. In applications, the temperature - composition diagrams of binary systems were faily reproduced, which are asymmetric and closed in a loop or have lower conslute points, and the multicomponent multiphase equilibria could be qualitatively predicted. In the calculation of the polymeric chain molecule systems, the effects of the chain flexibility and the limited solvation capability of the counter-solvent were lumped into the size estimation of the chain blob, or into the counting of the number of blobs in a chain. In water-PEG systems, a closed-loop diagram was also calculated by correcting the over-estimated size estimation in UNIQUAC on the basis of the blob rescaling concept.