Taking Fuling shale gas field of Sichuan Basin as an example, a method to effectively evaluate the gas content of horizontal well is discussed in Ordovician Wufeng Formation and Silurian Longmaxi Formation. According to a large number of drilling and production data of horizontal wells, and the main controlling factors of gas content in exploration wells, four parameters such as corrected total hydrocarbon of gas logging, pore pressure coefficient, porosity and gas content of log interpretation are chosen for evaluation. Based on samples of 53 wells with equivalent fracturing parameters in Jiaoshiba area, Fuling shale gas field, the four parameters are normalized with assignment method or maximum value method, and the weight of each parameter is calculated with grey correlation coefficient method, then the equation of gas content for horizontal well is setup. Based on the probability accumulation curve of the calculation results, the grading model of gas content is established. Thus a set of methods to quantitatively evaluate the gas content of shale gas horizontal wells is formed. The evaluation results of the other two horizontal wells with the method are in good agreement with the actual production data. It is proved that the method can appraise the gas-bearing capacity and effectively predict the testing output of horizontal wells in shale gas field.