Abstract: The Low-metamorphic rock series in vast areas from Heiheize Daban-Xai- dulla-Habak Daban-Kangxiwar-Dahongliutan to Quanshuigou on the southern slope of the Kunlun Mountains is a barren bed that remains controversial for a long time. When 1: 1, 000, 000-scale regional. geological surveys were carried out in 1982-1983, 13 fossil localities of Fustiaria, Thecosmilia, Pentagonopentagonalis and Baiern were found in the area, and meanwhile various kinds of fossils such as Fustiaria and Halobia were found to grow together in neighbouring areas. Therefore this low-grade metamorphic rock series is determined to be of Middle- Late Triassic age. The determination of the age of this bed provides grounds for defining the boundary between the Kunlun Mts. and Karakorum Mts. stratigraphic subre- gions, furnishes evidence for drawing the northern boundary of the Tethys Sea, and is of important significance for the study of the nature of the Kangxiwar fault, division into plates, laws of plate movements and the history of tectonic evolution.