Rear arc magmatism is a new term in our country and many of our documents discuss and translate it as “back arc magmatism”. Actually, rear arc is different from back arc which is no longer a part of arc structure, rear arc is still belong to arc environment. At present, the worldwide study of rear arc is very limited because it’s outcrops are less and the sign signature to identify it is still ambiguous. In this paper we try to introduce rear arc magmatism briefly and contrast the rear arc basalts（RAB）with typical island basalts（IAB）and back arc basalts. The study shows that, rear arc basalt is mainly composed of medium-high K alkaline and shoshonite series rich in Na2O, K2O, P2O5 and poor in CaO compared with typical IAB and BAB. The rear arc trace elements have the same signatures as typical island arc magma, but more enriched in LILE and HFSE, and it’s LREE is also obviously higher than the typical island arc magma. Compared with the typical island arc magma, rear arc magma has the same clear Nb-Ta negative abnormal. It’s hard to set this three basalts totally apart, but there is some differences between BAB and RAB, like Sc/Nb-Ba/Y, Cu/P2O5-Y/ZrlSc/Nb-Sr/Y, F2O3 /Zr-Y/Zr figures shows. The identify of rear arc magmatism complete the arc structure: from trench to arc direction, with the strengthen of slab subduction, increase of the depth of magma source and crust contamination, a complete arc structure should contain front arc, arc and back arc magmatism. While the back arc basin appears in the back of an arc as a result of oceanic crust extension. Meawhile, front arc mainly composed of Boninite, arc is IAB, rear arc mainly contains alkaline series and back arc usually made of MORB（+IAB）. Clearly, the come up of rear arc magmatism has a positive significance for rebuilt the ancient orogenic belt arc structure and determine the ancient subduction direction.