Abstract: According to the phenomenon of CO abnormal overrun of return airflow corner in the coal seam mining currently, the CO generation and sources law in coal seam mining was studied by field experiment. The results showed that the rising of CO concentration in the return airflow corner appeared mainly in the normal mining, in other words, the increase of CO concentration was closely related to the mining process. The original existence CO in the coal seam was one of the important causes for leading to the CO abnormal overrun of return airflow corner in the normal mining of coal seam in Fengshuigou Coal Mine and Laogongyingzi Coal Mine. Before and after coal body crushing and the degree of crushing had a great influence on the CO generation. The smaller the particle size of coal was and the larger the specific surface area, the more of the CO generation was. The main source of the CO of return airflow corner in the coal seam mining was the low-temperature oxidation in the coal body crushing process in the main coal seam of Fengshuigou Coal Mine and Laogongyingzi Coal Mine.