Two kinds of sparse aperture systems of three sub-apertures and three arms sparse aperture are researched, and the characteristics of this two kinds of sparse aperture configurations are analyzed. Modulation transfer functions (MTFs) of the three sub-apertures and three arms configurations are derived from the formulas of the pupil functions．Based on the formulas of MTF, MTF curves are simulated by Matlab. Comparing the MTFs of three sub-apertures and the three arms aperture, it is shows that MTFs of two kind of configurations are all arranged to uniform hexagon. When the fill factors are both at 20%, the MTFs of three sub-apertures and three arms aperture have zero frequency at the normalized spatial frequencies of 0.3 and 0.15, respectively. The MTFs of the two sparse aperture configurations become larger with the increase of the fill factor. The MTF curve of three arms aperture is more stable than that of three sub-apertures, but with smaller MTF values. As a result, three arms apertures lose more information. The results of imaging simulation and image enhancement of two sparse aperture configurations show that three sub-apertures configuration outperforms three arms aperture in imaging quality.