Orinus longiglumis L.B. Cai & X. Su sp. nova (Poaceae) is described and illustrated. It is endemic to the south-central part of Xizang Zizhiqu (Tibet), China, occurring at an elevation of 3040 to 3650 m on sandy soils. It resembles O. thoroldii, but differs from that species by the commonly hairy culms and leaves, longer panicles, longer glumes that are sparsely spinulose and pilose, longer anthers, and the paleas that are shorter than the lemmas. Orinus longiglumis differs from all other known species of Orinus by having glumes that are longer than or subequal to the adjacent florets.