Abstract: The accummulation and genetic mechanism for the deep-water pelecypod and ammonoid communities in the Middle Triassic Qingyan Formation (or Xinyuan Formation) are discussed in the present paper on the basis of palaeoecology and palaeoenvironments in southern and central Guizhou during Triassic time.The flourish,burial and preservation of the Kueichousaurus faunas were constrained by the major global regressions during the Ladinian and confined to the semi-enclosed gulfs in the special sigmoidal shoal zones of platform margins.The palaeoecological maps of the study area during the Olenikian,Anisian and early Ladinian are drawn in this paper.Four trace fossil assemblages and ichnofacies are established,and the models for the distribution of the conodonts and pelecypods from shallow-water to deep-water environments are herein suggested.