Through the study of regional geology, distinct differences have been found between the upper and lower parts of the Early Precambrian metamorphic rock series in the Yanliao area in respect to the environment of formation of the protoliths, protolith formations, metamorphic degrees and rock associations, strain features and deformation features. In the middle of the metamorphic rock series, there is an obvious interface, which divides the whole rock series into two parts. The petrological character between the upper and lower parts of the interface shows a sudden change. Gneissosity of the strata intersects at an angle locally. Showing the lower parts over lain and truncated by the upper ones. Thus the authors consider that the two parts of the rock series are in unconformable contact with each other. According to the isotopic data, the upper rock series belongs to the Early Proterozoic Hongqiyingzi Group (the upper part of the former Dantazi Group) , whereas the lower rock series still belongs to the Dantazi Group (the lower part of the former Dantazi Group). The discovery of this angular unconformity has certain practical significance in the stratigraphic classification, new group establishment and mineral reconnaissance and prospecting. It may serve as important evidence for studying the evolution of the Archean-Early Proterozoic crust in this area.