According to the data of geological exploration, the main geological factors of gas occurrence in No. Ⅲ3  coal seam of Xuandong No.2 Mine were discussed. Based on the gas geological theory, the factors affecting the coal quality of the coal seam, coal-bearing hydrocarbon generation capacity, gas content and gas occurrence were analyzed. The results showed that due to the invasion of magmatic rocks in Xuandong No.2 Mine, secondary hydrocarbon generation occurred in the coal seam, promoting the generation of gas, and deep burial of the coal seam with a certain impact on the occurrence of gas. The fault distribution had a certain influence on the migration and storage of gas. Among the control factors affecting the occurrence of gas, the main controlling factor was the invasion of magmatic rock. The general control factors were fault, coal seam depth and thermal evolution of coal thermal evolution degree.