A sparse-aperture design named dual three sub-apertures,which is composed of nine subapertures,is proposed. Each three sub-apertures make up of a sub-pupil,three sub-pupils make up of a main pupil. The configuration of dual three sub-apertures is symmetrical and redundant. The symmetrical sparse－aperture systems of three arms and dual three sub-apertures are researched. The feature and Modulation Transfer function(MTF) are compared between dual three sub-apertures' and three arms'.Image simulation and Wiener filter of the two kinds of symmetrical sparse apertures are illuminated with different fill factors,and image quality is evaluated. The nonredundant sparse aperture of Golay6 is also compared. The results show that the configuration and image quality of dual three sub-aertures are better than three arms'. The symmetrical configuration of sparse aperture systems has the advantages of flexible configuration and easy fabrication.