In the process of marine shale gas exploration，it is found that the gas contents of shales are related to the apparent resistivity，and the shale section with low resistivity generally shows poor gas content. In order to reveal the origins of the low resistivity of marine shales，the laser Raman，resistivity measurement by dried cores，charging effect observation by scanning electron microscopy（SEM），inclusion analysis，and organic geochemistry experimental analysis were carried out based on the well drilling，logging，and testing data from key wells in Southeast Sichuan area and its adjacent areas. In terms of organic matter carbonization and preservation conditions，the origins of the low resistivity of the shale reservoir were discussed in this paper，and the influence ranges were predicted. The results show that shales with low resistivity have three typical characteristics in terms of electrical，physical and gas-bearing properties. In high-quality shale sections，the shales have the resistivity with sudden or gradational changes，small pore diameters，low porosity and poor gas-bearing properties，and most wells are dry. For shales with a vitrinite reflectance（Ro）of over 3.5%，strong carbonization of organic matter is the main factor leading to low and extremely low resistivity. For shales with a Ro of less than 3.5%，the poor preservation condition is the main factor for the formation of low and extremely low resistivity，and weak carbonization has an important effect on the low resistivity. In the weak carbonization stage，the water content and water saturation of shales increase as the preservation conditions are damaged. Under the action of compaction，the pores and fractures collapse and close，and the matrix particles contact in inlay mode. So the electrical conductivity is enhanced，and the resistivity decreases significantly. As the abundance of organic matter gets higher，the resistivity becomes lower. The influence ranges of strong carbonization of organic matter are regional，and those of poor preservation conditions are relatively small.