Abstract：This paper briefly introduces the distribution, sedimentary formations, sedimentary environment, biotic province and tectonic deformation of the Triassic System, as well as its deformation difference from the adjacent geological bodies in the western Qinling. On that basis it discusses the evolutionary history of the study region. This region evolved quickly from the Yangtze-type neritic carbonate rocks in the stable environment to the Tethyan-type very thick abyssal flysch sediments during the short Middle Triassic geological evolution. It also discusses the tectonic features of the Tethyan taphrogeosyncline during the evolution from its opening and deposition through closing and stopping of deposition to rapid closing and folding. Finally the paper sums up the Triassic basin evolution pattern.