The gabbro of Xiji region belongs to the tholeiitic series, which has the characteristics of high Al, low alkali, low Ti and low P2O5. The gabbro is enriched in large ion lithophile elements (LILE) Rb, Sr, K, and high field strength elements (HFSE) Nb, Ta, Ce, Nd, Sm, Tb, Y and Yb are relatively low, and Nb and Ta are negative anomalies which shows characteristics of volcanic arc magmas formed on subduction zones. The LREE curve enriched REE right inclined, the type of curve is similar to island arc and back arc basin, it formed in the continental margin—arc environment. U- Pb zircon dating shows that LA- ICP- MS U- Pb zircon dating of gabbro was 437.0 + 2.8 Ma, which the age of formation is early silurian. Gabbro and granite of Xiji region has the same formation environment and very close with the zircon U- Pb age, and both of them are the products of magmatic activity during the same period. Combining regional geological information, It is concluded that the gabbro body ofXiji region is the product of plate subduction.During Late Ordovician—Early Silurian, the northern Qilian basin tends to be closed, the oceanic plate subducted and dehydrated, provided to the mantle wedge, peridotite is melted, leading to mantle upwelling and forming basic (gabbro) and acid (granite) pluton.  It is believed that gabbro of Xiji region and ophiolite belt in the gabbro of Huluhe group of Eastern Gansu, and Laohushan area of Jingtai in Gansu province is likely to be the product of tectono magmatism in the same tectonic environment. Xiji region may exist because of mixed rock ophiolite tectonic sequence damaged parts or disorderly deposits by means to regional comparison.