In this paper, the theorems of a symmetry axis, established by professor Tang Aoqing and professor Jiang Yuansheng, were expanded in a certain extent, and were described in the definite form. The expanded theorems of a symmetry axis not can decompose eigen polynomial of conjugate molecule with a n-fold rotation axis into products of nfactors, but also can derive the analytical expressions of π-Molecular orbital.

Key words: MOLECULAR ORBITAL THEORY, MOLECULAR ORBITAL PATTERNAL THEORY