Abstract: The present paper gives a detailed description of the structural features and genetic mechanism of the Duosang graben in the Ngari area,Xizang.Some speculations upon the genetic mechanism of the Duosang graben can be made on the basis of the structural development on both sides of the graben,and apatite and zircon fission-track age determinations.The rifting of the graben may be initiated during the Miocene,and continues to be active till the Quaternary.The N-S-trending compression of the Gangdise-Nyainqentanglha-Tengchong plate by the Indian plate resulted in the crustal uplifting first and then gravity sinking and lateral migration of the lower crustal matter.The E-W-trending extension led to the connection of some conjugate joints formed in the early stages and finally to the formation of the graben.The lateral regional faulting may have important effects on the width of the individual parts of the graben and inhomogeneity of subsidence.