The carbon and sulfur content, and the carbon isotopes of organic matter were analyzed for 61 outcrop samples collected from the Ordovician Wufeng formation to the lower Silurian Longmaxi formation in Bowangshan town, Xingwen County in Sichuan Basin, together with comparison with the results of Changning profile and Changxin 1 well, we studied the effect of weathering on shale gas index such as total organic carbon (TOC), sulfur content and organic carbon isotope (delta~(13)C_(org-PDB)). The results showed that TOC content is high (2.28% to 5.06%) with an average of 4.01% in the Wufeng formation and lower part of the Longmaxi formation in Xingwen area, and the thickness of the high TOC interval is about 25 m. TOC content sharply decreases from 0.83% to 1.93% in the upper part of the Longmaxi formation. The delta~(13)C_(org-PDB) values are concentrated in the range of -31.5 to -28.8, with an average of -30.3. The distribution range and vertical change characteristics of TOC content are comparable with Changning profile and Changxin 1 well, indicating that high evolutionary residual organic matter in Wufeng formation and Longmaxi formation have highly aromatized and weathering resistance, basically not affected by weathering. Sulfur contents range from 0.02% to 3.15%, and it is far lower than Changning profile in bottom 20 m interval. It indicated that pyrite in high organic matter layer shale has basic loss (< 0.1%) influenced by weathering. Sulfur content for the inversion of organic matter sedimentary environment has lost effectiveness. There is a negative correlation between TOC and delta~(13)C_(org-PDB) values. With the increase of TOC, delta~(13)C_(org-PDB) values decrease, showing that the reducing conditions benefit for preservation of organic matter enhanced. Combined with petrology and geochemistry characteristics of the Wufeng and Longmaxi formation, we suggest that the main controls to the organic matter enrichment are sea level rising caused by global warming and the deep water reducing environment favorable for preservation of organic matter. The Wufeng Formation and the lower part of Longmaxi formation marine shales with abundant TOC content in Southern Sichuan sedimentary center is the main target for shale-gas exploration.