The northwestern China is composed of several terranes，where the tectonic movements are complexBecause of the lack of paleontological proof，the recognition and relegation of paleobiogeographical division still remain to be solvedBased on the analysis of fauna characters，the authors studied the Middle  and Late Cambrian and Ordovician fauna nature of different stratigraphic provinces in Qilianand Qinling areas，as well as relegation of paleontological types，and ascertain the distribution of faunas of transitional type in Qilian and Qinling areasAccording to the analyses in geodynamics and paleogeography researches，twopossible reasons，which resulted in the similar faunas of transitionaltypes between the Qilian and Qinling areas and South China during the Middle and Late Cambrian and Ordovician，are discussed One is that Tarim Plate lay to the west of Yangtze Plate,SinoKorean Plate lay to the north of the Yangtze Plate,the Qilian andQinling areas were situated between the Yangtze Plate and Tarim Plate during the Middle and Late Cambrian and Ordovician，and were qualified for interchange between South China fauna and North China fauna，and thus roughly similar faunasemergedAnother is that there were some terranes，which were situated along northern margin of the Yangtze Plate in the Qilian and Qinling areas during the Middle and Late Cambrian and Ordovician，and the faunas or biotic types，which were similar to those in southern margin of the Yangtze Plate，were developed on the terranesBefore the Mesozoic，the slip movement between the main part and the northern margin of the Yangtze Plate caused the mainpart of the Yangtze Plate to shift several hundred kilometres eastwardBut the movement of the terranes of northern margin of the Yangtze Plate，which belonged to the Qilian and Qinling areas，was within a narrow rangeTherefore，the current situation，that the transitional faunas or biotic types appeared in the Qilian and Qinling areas and the transitional zones along the northern margin of the Yangtze Plate were absent，was created