Back-Arc Basin Basalts(BABB) distribute narrowly in the world. Currently, BABB are mainly distribute in the western Pacific Ocean outside the island arc in small scales and short lifespan which are related with subduction. It is generally considered that geochemical compositions of BABB vary in a large scale, including N-MORB, E-MORB, IAB, and a small amount of OIB. In most of basalt discrimination diagrams, BABB mainly fall into MORB area, suggested that BABB are similar to MORB. New data of MORB shows that MORB contain a series of constituents from MORB to OIB, also IAB, while BABB are mainly composed by MORB and IAB, rarely show OIB components. BABB is generally analogous with MORB whereas the former is enriched in Cs, Rb, U, Ba, Th, Pb, and other incompatible elements, exhibits an obvious Nb-Ta negative abnormal, suggesting that BABB is featured with both geochemical characteristics of MORB and IAB, with subuduction sediments partition during its magmatism process. It is mainly formed by partial melting in wet environment. Back-arc basins are divided into two groups: mature ones and immature ones. Primary back-arc basins share some geochemical characteristics of island arcs while mature back-arc basins exhibit few IAB features and is closer to MORB.