Abstract: Layered Mafic-ultramafic intrusions, which carry abundant information of mantle and provide an excellent approach to probe the mantle material composition, plate tectonic and deep geological process, are generally considered to be an important symbol of lithosphere extension, We discovered a suit of layered Mafic-ultramafic intrusions in Southwest Tianshan area, and obtained the zircon U-Pb age of gabbros of 224±4 Ma. These rocks are characterized by the enrichment of LREE, H₂O, Na₂O+K₂O and incompatible elements such as Th, U, Nb, Ta, etc., and depleted in HREE. They might be derived from enriched mantle, which is formed by low degree partial melting of garnet lherzolite. The primary magma may be high Mg basaltic magma which was rich in iron and titanium and mainly controlled by the fractional crystallization. This magam in the continental orogenic stage was actived in the environment of intracontinent orogen after the closure of the South Tianshan ocean and post collisional orogeny, which derived from mantle in the envirnment of extensional environment. We can concluded that the Southwest Tianshan area was under an extensional tectonic seting during late Triassic.