Through measurement of the total organic carbon content (TOC), mineral composition and high-pressure methane isothermal adsorption of 6 marine shales and 2 silty mudstone samples of the Lower Cambrian Qingxi Formation in the Maoershan section in northern Guangxi, South China, the methane adsorption performance of the shales is evaluated and its influencing factors are discussed. The experimental total organic carbon results show that these samples have high TOC values, with an average value of 6.57%. The experimental results of the mineral composition characteristics show that quartz content in the samples of the study area is relatively high, its distribution range is 42.3%~69.1%, and that quartz is the dominant mineral. The samples of the Qingxi Formation also have a high clay mineral content, with a distribution range of 12.4%~32.7%, with an average value of 20.8%, so clay is the second-most common mineral. The other minerals include mainly feldspar, mica and siderite. Through linear fitting analysis, the fitting R2 value of the linear regression equation between the maximum absolute adsorption capacity of methane and TOC content of shale in the Qingxi Formation in the study area is 0.8328, indicating that the TOC of shale samples in the study area has a direct impact on the maximum absolute adsorption capacity of methane. It means that the methane adsorption capacity is positively correlated with the TOC content. At the same time, there is also a good positive correlation between the maximum absolute adsorption of methane after TOC standardized treatment and clay minerals. As a result, the TOC content is the main factor affecting the methane adsorption capacity. The second most important factor affecting the methane adsorption capacity of the shales is the content of clay minerals, and its influence is relatively weak. In addition, through comparison, it is found that at the same TOC content, the maximum adsorption capacity of the shales is basically consistent with that of the shale of the Cambrian Longmaxi Formation shale in the Sichuan Basin, Southern China, indicating that the shale of the Lower Cambrian Qingxi Formation in the study area has similar methane adsorption performance to the Cambrian Longmaxi Formation shale.