The convergence boundary between the East Kunlun terrane and the Bayan Har-Songpan Garze terrane of the Northern Tibet plateau is a large transpressional zone at the south margin of the East Kunlun Mountains. The deformation structures are different between the eastern segment (A' nyemaqen segment) and the western segment (eastern Datan and western Datan segment). The structures of the A'nyemaqen segment are characterized by superimposed thrust slices with southward erogenic polarity formed during the stage of Indosinian collision-orogeny and brittle sinistral strike-slip faults formed during Cenozoic. The eastern Datan and western Datan segment consists dominantly of an E-W-trending ductile sinistral strike-slip transpression zone com-panied by a NW-SE-trending fold and fault zone at its both sides, which formed 220 Ma ago. The ductile deformation continued till 220 Ma B. P. and then the deformation was manifested by the reactivation of the brittle sinistral strike-slip deformation structures. Therefore, the large convergence zone at the south margin of the East Kunlun Mountains is a very special tectonic zone which changed gradually from the " constrictive compression" in the eastern segment to the "transpression" in the western segment. Its formation was related to the northeastward oblique subduction of the Bayan Har-Songpan Garze terrane beneath the East Kunlun terrane since the Indosinian.