A polymetallic Ni- Mo layer at the base of the Niutitang Formation (and its equivalents) in the lower Cambrian of South China, serves as a marker bed for regional correlation of lower Cambrian strata. However, up to now, the precise stratigraphic position of polymetallic Ni- Mo layer is uncertain for some sections in South China, which hinders the precise correlation of stratigraphic and makes our interpretation of the paleo- ocean changes unsolid. In this study, we collected rock samples from the Meishucun and the Pingyin section and conducted trace element analysis using inductively coupled plasma mass spectrometer (ICP- MS) with identifying of the precise position of polymetallic Ni- Mo layer in two sections. Furthermore, the samples from the base of the Niutitang Formation in the Pingyin section were analyzed for Fe speciation. Combined with previous data, our data reveal the redox condition of the seawater in Nanhua basin during the deposition of polymetallic Ni- Mo layer (~521 Ma). Trace- element content results show: Ni, Mo peaks (Ni: 135. 00×10-6, Mo: 583. 00×10-6) with the basal Yuanshan Formation (3 m above the base boundary) at the Meishucun section and maximum Ni, Mo concentrations (Ni: 2480. 00×10-6, Mo: 16341. 00×10-6) at the base of the Niutitang Formation (2. 5 m above the base boundary) at the Pingyin section. Therefore, we suggest that the polymetallic Ni- Mo layer should lie within the basal of the Yuanshan Formation (3 m above the lower boundary) at the Meishucun section, and the polymetallic Ni- Mo layer should lie within the base of the Niutitang Formation (2. 5 m above the lower boundary) at the Pingyin section. Fe speciation of samples from the Pingyin section indicates that the seawater euxinia information (FeHR/FeT＞0. 38, FePy/FeHR＞0. 80) was recorded in the polymetallic Ni- Mo layer (or near strata) at the Pingyin. Combination with previously published Fe speciation data from the polymetallic Ni- Mo layer (and near strata, or its equivalents) of representative sections in South China, reconstructing the redox condition of seawater during the deposition of polymetallic Ni- Mo layer in Nanhua basin (including the platform, slope and basin zone). Indicating that an extensification of euxinia deep seawater occurred in Nanhua basin during this period. This event may have a profound impact on Cambrian life episodic radiation.