The nature of prototype basin of late-Triassic was discussed by studies in areal tectonic framework, rock tectonics and sedimentary formation in Qiangtang area. The Triassic basin formed in the inoculation stage of neotethys branch ocean basin. The geochemical characteristics of magmatic rock showed that the deformation circumstance was intraplate tension. The central uplift and the north and south depressions formed in different periods. Most of the geologic facts had no brief for the viewpoint that this basin was a foreland basin, which was generally accepted before. According to these studies, the late Triassic basin nature of Qiangtang area was identified as quasicraton basin.