Abstract: It is difficult to accurately evaluate clay minerals, including those that contain clasolite and carbonates by using conventional logging methods.The crystal detector of the ECS logger measures gamma rays produced by collision of neutron sources and the strata minerals, so the ECS element log response equation was established according to the corresponding relationship between minerals and gamma rays. The optimized inversion method was used to determine mineral types, and calculate mineral content, grain density and brittleness index. By using this method, the ECS logging data of Well X in shale gas block A was interpreted, the elements including Si, Al, Fe, Ca, Su and K were selected to determine six to eight kinds of minerals and their contents, related to 10 minerals such as quartz, feldspar, limestone, dolomite, illite, chlorite, montmorillonite, pyrite, mica and anhydrite. Eventually, the inversion results coincided well with the core mineral analysis results, the grain density of the shale formation in this well was calculated according to the contents of the minerals, which ranged from 2.65-2.75 g/m3, the brittle index is 40-60. It showed that shale formation minerals and their contents can be evaluated by using ECS logging data, and the grain density and brittleness index of shale formation can be calculated. These results could provide an accurate evaluation for shale formations and guide shale formation fracturing.