Abstract: Abstract：Based on the urban bedrock geological mapping and research on the section, the Middle-Lower Ordovician Nanshanshang section in Banqiao Township, Lin'an City, was chosen as the candidate stratotype. According to the stratigraphic sequence, lithologic association and boundary markers, combined with the general characteristics of regional changes, four formation-rank lithostratigraphic units were redefined and distinguished. The stratigraphic age of the section was determined to be Early-Middle Ordovician according to the stratigraphic and fossil correlation of the Jingshan Range and Banqiao sections. This redefinition is of great significance for the reconstruction of the stratotype section, protection of geoheritages, lithostratigraphic mapping and exploitation and utilization of Ordovician limestone resources.