Due to the lack of reliable discovery and systematic study of SSZ ophiolite and Intra- oceanic arc igneous rock, which restricts the further understanding of the Paleozoic subduction extinction process of the eastern part of the paleo Asian ocean. The Bagahaer Early Carboniferous diorite distributed along the Hegenshan suture zone in the eastern part of the Xingmeng Orogenic Belt was discovered to be outcropped in the northern section of Diyanmiao SSZ ophiolite in Xiwuqi, Inner Mongolia. It belongs to Calc alka series, chemically characterized by 57.71%~61.24% of SiO2, 15.58%~16.68% of Al2O3, and 3.30%~4.23% of MgO, with relative rich in Na2O (3.29%~4.15%) poor in K2O (1.05%~1.69%) and high ratio of Na2O/K2O (2.18~3.95). The diorite relatively enriched large ion lithophile elements (LILE) Rb、Ba、K and depleted high field strength elements (HFSE) Nb、Ta、P and Ti, etc. In addition, it features low ΣREE (85.19×10-6~98.21×10-6) and clear REE fractionation ((La/Yb)N=3.08~3.99), without obvious Eu anomaly (δEu =0.61~0.82). Eighteen zircon grains from the diorite yielded a weighted mean 206Pb/238U age of 324.2±1.8 Ma, indicating an Early Carboniferous age. The petrological and geochemical characteristics of the diorite have obvious similarities and progressively evolved relationships with the fore- arc basalt (FAB) and boninite in the Diyanmiao SSZ- type ophiolite. The discovery and confirmation of Bagahaer Early Carboniferous intra- oceanic arc diorite in the Diyanmiao SSZ- type ophiolite reveal the transition from initial arc to mature arc of the eastern Paleo- Asian Ocean intra- oceanic subduction during the late Paleozoic.