Abstract: The Yunzhug sheeted dike swarm is located between the Bangong Co-Nujiang suture zone in northern Tibet and Yarlung Zangbo suture zone. Its large scale and complete structure preserved are rarely seen in China. The sheeted dike swarm consists of meta-diabase, meta-gabbro and meta-diabase porphyrite dikes and upward it has gradational and intrusive contact relationships with pillow basalt. The chilled border is developed on one side or two sides of the swarm. Their chemical composition is characterized by high contents of CaO, AI2O3, MgO, FeO and Fe2O3 and low contents of TiO2 and P2O5. They belong to the subalkaline series. The trace elements main manifestation MORB characteristic, manifestation MORB and IAT transition characteristic in the part differentiate diagram, guess may generate from back-arc basin environment. According as the radidarian cherts times and isotope ages of the dike swarm assurance that the Yunzhug sheeted dike swarm may have formed in the Middle Jurassic-Early Cretaceous.This discovery provides new evidence for seafloor spreading in the Meso-Tethys Ocean period.