By using a numerical exact diagonalization method, the properties of atomic clusters with atom number N=5 and N=6 are investigated in the framework of the extended Hubbard model. The optimized structure and the corresponding total spin S are obtained both as a function of Hubbard onsite interaction U, nearest-neighbor Coulomb repulsion V and filling number of electrons. Results show that with V increasing, the optimized structure of cluster turns into a chain or star-like structure with fewer bonds. The thermodynamic properties are also analyzed based on the distribution of energy levels of cluster with an optimized structure.