The Lower Cambrian is the main target intervals of marine shale gas exploration and exploitation in China. Shale gas content varies greatly in different intervals and how to determine favorable targets is an important problem to be solved urgently. Taking Well XN-1 in Xiuwu Basin as an example，according to core description，logging data analysis，mineral and elemental composition analysis and total organic carbon（TOC）content tests，the shale in Lower Cambrian Wangyinpu Formation and Guanyintang Formation was studied. Results show that water redox conditions and bioproductivity control the enrichment of sedimentary organic matter. Hydrothermal activities are helpful for the increase of reducibility of seawater and enhancing bioproductivity，and thus controls the enrichment of sedimentary organic matter and the enrichment of shale gas is further affected. The water reducibility during the deposition of SQ1 at early Cambrian varies greatly，and it is generally strong during the deposition of SQ2 and SQ3 of the Wangyinpu Formation. The reducibility of all the three sequences is stronger than that during the deposition of SQ4 and SQ5. The bioproductivity during the deposition of SQ3 is the highest and little difference in the bioproductivity has been found between SQ1 and SQ2，both of which show higher values than that of SQ4 and SQ5. Siliceous origin of SQ1 varies greatly in the study area；most siliceous minerals of SQ2 and SQ3 are hydrothermal origin，whose content is high；content of hydrothermal origin siliceous minerals drops in SQ4 and terrigeneous siliceous content increases；siliceous minerals of SQ5 originate from normal terrigeneous clastic deposition. SQ2 and SQ3 are favorable targets of shale gas in the Lower Cambrian.