This study reported newly discovered Triassic basalts in the Langshan region, analyzed its tectonic setting and contemporaneous deformation, and discussed the characteristics of the Late Triassic basin in the northwest margin of Ordos basin. 40Ar/39Ar geochronology show that the basalts formed in the Late Triassic (217 Ma). Whole- rock geochemistry reveals that the basalts have OIB affinity, derived from the 5%~10% partial melting of garnet and spinel lherzolite, formed by the decompression melting of the asthenosphere in the intraplate extensional setting. The Langshan region also developed a Late Triassic NE- SW trending ductile sinistral shear zone, which connected southward with a simultaneous sinistral shear zone in the Bayanwulashan and Helanshan regions and extended northward into Mongolia. Temporal simultaneity indicates the close relationship between sinistral shearing and basalts eruption. By comparing the contemporaneous basalts, Yanchang Formation, and sinistral strike- slip faults in the Langshan and Helanshan regions, we proposed that the northwest margin of the Ordos basin was under the far- field effects of the collision of North China Plate and South China Plate in the Late Triassic, and the sinistral ductile strike- slip lead to the formation of regional pull- apart basin, accompanying the extension of lithosphere and the basaltic magmas eruption resulted from the decompression of asthenosphere.