Objectives: Since the precambrian period in Altay, there have been many tectonic — magmatic events, and formed large areas of granite. These granite bodies are believed to be mainly formed in late Paleozoic. Recently, some early Paleozoic and Mesozoic granite bodies were found. However, the study on the tectonic background and genetic mechanism of mafic intrusion in the region is weak. In this paper, we studied on the newly discovered mafic intrusion body systematically, the new evidence will be provided for the tectonic—magmatic activity of Altay in early Paleozoic. Methods: Based on detailed observations of Qibaroi mafic intrusion in western of Altay mountains,we have studied the petrology, geochemistry and chronology of Qibaroi rock. The geological implications of Qibaroi mafic intrusion was discussed.  Results: The Qibaroi mafic intrusion including finegrained gabbro, hornblende gabbro, hornblende norite and finegrained norite, the zircon UPb age of hornblende gabbro is 470.6+4.3Ma,which was identified the Middle Ordovician mafic intrusive rocks in the North Altay orogenic region for the first time. In the diagrams of SiO2— (Na2O + K2O) and SiO2—K2O, it is shown as a calcium alkaline rock series, the sample contains relatively low high field strength elements (HFSE), Nb has a slight loss, and has the characteristics of light rare earth enrichment, it is shown that Qibaroi Mafic Intrusion is influenced by the crust and has the characteristics of subduction. According to regional magmatic geochronology and geological characteristics, combined with the geochemical data of the Qibaroi mafic intrusion rocks, it is believed that the mafic magma may be formed in the back arc extension environment on the margin of continental plate, formed in the the paleo Asian Ocean northward subduction, the separation of plate from deep mantle leads to the interaction between asthenosphere mantle and overlying metasomatic mantle, and it is intruded into the weak zone.  Conclusions: The Qibaroi mafic intrusion forms on the edge of the continental plate, and its formed time is 470.6±4.3Ma, which was identified the Middle Ordovician mafic intrusive rocks in the North Altay orogenic region for the first time, it provides new information for the study of regional tectonic evolution.