Abstract: MORB, OIB and IAB (arc calc-alkaline basalt) have aroused much interest among geologists, with particular attention paid to igneous activities in island arcs related to plate subduction. Such island arcs can be divided into island arc and continental margin arc (active epicontinental arc). This paper discusses the IAB, mainly focusing on the identification of IAB. The IAT (island arc tholeiite) and the IAB are products of the fore-arc, the island arc and the rear-arc magmatism. Among them, the rear-arc is more diversified in composition and is different from back-arc (back arc):the former belongs to the scope of the arc, while the latter is related to the subduction system in the kinetics of formation; nevertheless, the back-arc is an independent tectonic unit, although its magmatism might still be affected by the subduction metasomatic fluids. Previous researchers made detailed studies of the IAB and put forward a variety of tectonic environment discrimination diagrams which have been widely used. In this paper, the authors tried to apply the global basalt data to verify the credibility of the discriminant figures. However, there only exist very few highly credible discrimination diagrams, and these figures are mostly related to Th, Ta (Nb), and Ti elements, such as the figures of Hf -Th-Ta (Nb), TiZr-Sr and Th/Yb-Ta/Yb, whereas the rest of the discriminant figures are of low credibility and characterized by multiple solutions, and hence should be used prudently. Researches show that the difference between the IAB and MORB, OIB mainly finds expression in the depletion of Nb-Ta, and this suggests that the most important criterion to distinguish the IAB from MORB and OIB is whether they are affected by subduction fluids or not.