Objectives：The Cathaysian flora has long been known as one of the four major floras during the Carboniferous and Permian times, but the origin of the flora still remains as yet unsolved. Methods:Based on a systematic study of the Late Namurian (Bashkirian) flora in the east sector of North Qilian Mountain, there are 33 genera and 95 species as endemic elements (genera, species) accounting for more than 80% of the floral composition. Results:There are many typical elements of Cathaysia Flora, for example, (1) Oriental Lepidophytes take up about 25% of the flora, including Cathaysiodendron from the Early Carboniferous, various Oriental type of Lepidodendron , Bothrodendron and Sigillaria brardii . (2) Sphenophyllum lungtangense and Sphenophyllum ? ( Tetrafolia ) changshaense , which appeared since Late Devonian, the Early Carboniferous Sphenophyllum jingyuanense , the Late Namurian Sphenophyllum emarginatum . All these species with long cuneiform leaf lamina appeared much earlier in Cathaysia than in Euramerica, from which Permian Lobatannularia might have evolved. (3) Tingia and Conchophyllum had long been regarded as typical representatives of the Cathaysia Flora. Tingia appeared since late Early Carboniferous, and till to Late Namurian (Hongtuwa Formation) three species existed. (4) Many types of Paripteris and Linopteris , which flourished in middle and late Early Carboniferous, were still very common in early and middle Late Carboniferous. This is the most prominent feature in the early stage of Cathaysia Flora. (5) Mariopteris ( Karinopteris ), which occurred from Early Carboniferous continuously well developed, might be the remote ancestral group of Gigantopterids. Conclusions: This shows the Late Namurian flora in the east sector of North Qilian Mountain was in the early stage of evolution of the Cathaysia Flora, and the Late Devonian Shaliushui Formation, the Early Carboniferous Chouniugou Formation, the Late Carboniferous Tsingyuan and Hongtuwa Formations, together with Yanghugou Formation were the geological period of the evolutionary succession from Procathaysian Flora to the Cathaysia Flora. The east sector of North Qilian Mountain also became an early developed and prosperous area of the Procathaysian Flora and the Cathaysia Flora. It is proved again that the east sector of North Qilian Mountain might be the center of origin and early evolution of the Namurian Cathaysia Flora.