The Tibetan Plateau, which is made up of a number of terranes, has the world's most thick crust. There is a long-term dispute concerning crustal thickness across the Bangong-Nujiang suture (BNS) from the Lhasa terrane to the Qiangtang terrane. This paper mainly reports the result of the study of deep seismic reflection profile in this area. A clear reflection of Moho was detected, which reveals the change of crustal thickness from the Lhasa terrane to the Qiangtang terrane. Moho exhibits a sharp decrease of 6.2 km across the BNS and becomes 12.5 km shallower from the northernmost Lhasa terrane to the south Qiangtang terrane at 28 km north of the BNS. The viewpoint based on deep seismic reflection data denies previous understanding of a 20 km offset.