Abstract: During drilling the deep shale gas horizontal wells in the Weirong Shale Gas Field in southern Sichuan, it is very difficult to accurately identify the marker bed, determine the bit position and judge the penetrating state of bit. To solve this problem, the X-ray fluorescence (XRF) element mud logging data was used to establish a three-terminal chart, an element intersection chart and a three-dimensional element display chart, as well as a quantitative calculation model of evaluation parameters such as rock density and gas content. The Geosteering Technology has been formed by such principle, including that fact that a three-terminal chart was used to identify the key marker beds before window-entering, the element intersection chart was used to guide the accurate window-entering of horizontal well, the three-dimensional element display chart was used to determine the penetration of the bit in a horizontal section, and the shale density and gas content etc., were used to guide the optimization of horizontal wellbore trajectory. This technology has been applied in 18 horizontal shale gas wells in the Weirong Shale Gas Field, with the average drilling rate of the target up to 98.06%. Research results showed that the technology could improve the rate of encountering high-quality reservoirs by accurately identifying the marker bed, determining the bit position and judging the penetrating state of the bit.