The lower Hongshuichuan Formation is mainly distributed around Tuosuo River between Middle Kunlun orogen and South Kunlun orogen in eastern Kunlun Mountains. In this paper, the authors made a comparative study of the conglomerate of Lower Hongshuichuan Formation distributed in Baoriherie area and Kekesha area in components, psephicity and granularity of gravel. The results show that the main components of the gravel are limestone and metamorphic rock in Kekesha area. The main components of gravel in Baoriherie area are granite and metamorphic rock. LA-ICP-MS zircon U-Pb dating of granite yielded magmatic crystallization age of(464.9 ±9.3) Ma(MSWD=2.9) from Baoriherie area. The characteristics of gravel show that the source of the Kekesha area is Halaguole Formation in Qingshuiquan area, whereas the source of the Baoriherie area is Caledonian magmatic rock. These data indicate that the source of Lower Hongshuichuan Formation is Caledonian magmatic rock rather than arc granite of late Hercynian-Indosinian period. Combined with previous data, the authors hold that the Buqingshan-A'nimaqing Ocean began the northward subduction in late Permian, and the Hongshuichuan Formation was a set of sedimentary products in the fore-arc basin. It is held that Buqingshan-A'nimaqing Ocean began its subduction in early Triassic.