Abstract: A typical small accretionary wedge develops in Mayin'ebo region, east Junggar. Gabbro rock in the accretionary wedge block has high Al₂O₃(14.38%-16.33%), high TiO₂(1.81%-2.46%) and poor K₂O(0.17%-0.63%)geochemical characteristics. It is relatively enriched in LILE(Sr, K, Rb, Ba), and has no obvious anomaly in HFSE(Nb, Ta, Zr, Hf) content, moreover, the material source is identical with oceanic ridge basalt. Mafic rocks have similar E-MORB and OIB REE pattern, and no significant loss of Nb, Ta, Ti appeared, indicating that the process of its formation may not have been or weakly affected by the subduction zone. Comprehensively, such mafic rock of accretionary wedge is likely to come from the oceanic crust subducted seamount fragments proliferation process. According to material composition characteristics and previous geochronology evidence, Mayin'ebo accretionary wedge was formed in the post-Paleozoic accretionary wedge arc basin, the subduction accretionary complex was formed before the late Devonian.