Three dimensional elongation (3D-ELG) method is introduced to perform the calculations on real large systems based on regionally localized molecular orbitals. The settings are firstly justified by a quasi-one dimensional system calculations at HF/STO-3G basis set. Then two model systems are employed and calculated to validate the accuracy of 3D-ELG method at HF/6-31G basis set. The average deviation of the total energy between elongation and conventional calculations is 4.7 x 10 (7) au/atom for these two model systems. This small deviation indicates the feasibility of 3D-ELG scheme for the large molecular calculations. Finally, the further development of 3D-ELG method is pointed out. (C) 2012 Elsevier B.V. All rights reserved.