The relationship between Xiaoquangou group of the Middle-Upper Triassic and underlying Cangfanggou group of the Lower Triassic in Junggar Basin has been considered to be conformable and continuous. However, a great number of information indicate that the central and northern parts of this basin belong to a large unconformity in regional distribution, and the upper Cangfanggou group is absent to a large extent except for the southern area of the basin. The key for thoroughly solving this big problem attributes to the drillings of Moshen-1 well and Shimo-1 well.