Geometric structures of (SiO2)n-(n≤7)anion clusters are optimized by using the generalized gradient approximation density functional theory. The energy and vibrational frequency have been calculated. The lowest energy (SiO2)4- cluster is found to be more thermodynamically favored compared with other neighboring sized cluster isomers. Additionally,the lowest energy (SiO2)n-(n≥4)clusters grow up regularly based on the lowest energy (SiO2)4- cluster.