Shale gas proven reserve declaration in Fu ling Gas Field needs to calculate mineral percent with relatively high accuracy. According to core analysis, X- ray diffraction experiments and digital core technology, a simplified volume model is setup, in which rock skeleton is similarly composed of siliceous, carbonate and clay minerals. A new parameter of "apparent skeleton density of clay" is introduced and thus a new formula is setup to calculate percent of minerals in Lower Silurian Longmaxi gas-bearing shale reservoir. According to data of core analysis including X- ray diffraction, porosity and TOC, a series of charts are setup. With common log data, TOC can be calculated firstly, then the “apparent skeleton density of clay” can be obtained. Furtherly, the percent of major minerals suitable to the simplified model can be calculated with the formula. It is proved that this new logging calculation method is reasonable and useful with high accuracy and low cost.