Abstract: The diabase dike swarms found in the Yishan Lake-Daoliugou zone, Xijir Ulan Lake area, Qinghai are emplaced in the metamorphic quartz sandstone and feldspar quartz sandstone in the Devonian Lazhuglung Formation, and grayish white muscovite quartz schist and biotite quartz schist in the Proterozoic Ningduo Group. The rock types include diabase and gabbro-diabase, which exhibit the crystallization differentiation of the magmas, and may be traced back to the Late Devonian. These diabase dike swarms, just like the basic dike swarms in (Kejuezargen), eastern Heka Mountains, Qinghai, may record the crust-mantle evolution in the Hoh Xil region, and attest to the breakup of the palaeocontinent and initiation of the Xijir Ulan Ocean.