Trigonotis motuoensis, a distinct new species endemic to Xizang, China, is described and illustrated. It can be easily distinguished from all other known congeneric species by the ebracteate inflorescences, broadly spatulate calyx lobes and obliquely trigonous-tetrahedral nutlets that have flat bottom surface and triangular abaxial surfaces. Our molecular phylogenetic analysis based on nrITS confirmed that it belongs to Trigonotis sect. Elongatae. An updated key to the species of Trigonotis from Xizang is also provided.