The Daduhe Formation is a lithological unit in the Upper Ordovician rocks of western Yangtze Platform. It was established based on the section at Jiaodingshan of Hanyuan County, Sichuan Province. However, the lithology of the Daduhe Formation at the type locality is quite unique owing to its thin thickness, restricted distribution,and the presence of manganese ores. A newly found section at Wanhe of Yongshan County includes Upper Ordovician through Lower Silurian strata, cropping out along a country road near the Heping Village of Yongshan County, NE Yunnan,where the lithological succession across the Ordovician-Silurian boundary consists of, in an ascending order,the Daduhe Formation, the Kuany-inchiao Bed and the Lungmachi Formation. Lithologically,the Daduhe Formation can be subdivided into two members. The Upper Member is composed of calcareous mudstone,intercalated with argillaceous limestone and, the Lower Member consists of limestone interbedded with mudstone. Fossil groups of these strata include graptolites,brachiopods,trilobites,conodonts, chitinozoans and acritarchs. The graptolite succession of the Daduhe Formation is divided into,in an ascending order, the Dicellograptus complexus Biozone,the Paraorthograptus pacificus Biozone (including the lower subzone,the Tangyagraptus typicus Subbiozone, and the Diceratograptus mirus Subbiozone), and the Metabolograptus extraordinarius Biozone. Chitinozoans are assigned to the Eisenackitina ripae Biozone in the lower member. A brachiopod fauna, including Kassinella sp.,Leptellina sp., Paromalomena sp.,etc. and referred to a depth of BA5, is obtained at the basal Upper Member and such a deep-water brachiopod fauna has not been discovered from the contemporary strata in other areas of South China. The Daduhe Formation is of late Katian age (Late Ordovician) based on graptolites,brachiopods, and chitinozoans,corresponding to the span from the D. complexus Biozone to the basal M. extraordinarius Biozone. The Kuanyinchiao Bed bears the Hirnantia fauna,indicating a depth of BA3. The present paper emends the Daduhe Formation on the basis of the Wanhe section of Yongshan County and other sections in the western Yangtze Platform. Furthermore,the Wanhe section is proposed here to be an auxiliary section for the Daduhe Formation in consideration of its good exposure and prolific fossils. The emended Daduhe Formation is distributed in the western Yangtze Platform (NE Yunnan and SW Sichuan) and adjacent to the Kangdian Oldland. It can be correlated with the Wufeng Formation in the inner part of the Yangtze Platform, and much of the Tiezufeike Formation and the Daqing Formation (upper part) in the southwestern margin of the Yangtze Platform. The interval from the basal Upper Member of the Daduhe Formation (bearing brachiopods of BA5),to the Kuanyinchiao Bed (yielding Hirnantia fauna of BA3), and further upsection to the black shale of the Lungmachi Formation, fully reflects the rapid global cooling (the first pulse) and then warming (the second pulse), and an eustatic sea-level falling and then rising in the Yangtze Sea during the end-Ordovician mass extinction.