Abstract: To study regional tectonics in the midwestern Tibet plateau, the data of areomagnetic anomaly suveryed from 1998 to 2000 is reprocessed by upward continuation method. The results of different upward continuation levels reveal a significant anomaly of a subtle fault which located between the northern margin of Lhasa terrane and south side of Banggonghu-Nujing Suture, about along Geji North to Gaze South to Cuoqen North to Shenza North, from west to east. Combined with other results, this subtle fault, together with Jiali strikeslip fault, forms a largescale E-W strikeslip fault in the central Tibet. And the conclusion is also supported by other evidences from surface geology, geophysics and modeling. The E-W strikeslip faults control the force distribution and deformation within Tibet plateau.

Key words: central Tibet, areomagnetic anomaly, upward continuation, subtle E-W striking fault