Abstract: In order to solve the problem of CO abnormal overrun in air return corner of fully mechanized coal mining face, taking Shendong Mining Area as an example, through the comparison between the desorption experiment of CO in reducing environment and oxidation experiment of CO in oxidizing environment at normal temperature for coal of gob, which proves that the coal oxidation is the main factor to produce CO at normal temperature in the gob of Shendong Mining Area. Furthermore, after the investigation and field observation, we ascertain the internal factors of some coal seams, facilities factors and environmental factors causing CO overrun. According to different factors, we come up with the corresponding methods for CO overrun to ensure the safety production in the working face.