Abstract: In order to find out the laws of air leakage in goaf of fully mechanized top coal caving face in extra thick seam, taking Tongmei Guodian Tongxin Coal Mine Company as the research background, tracer gas technology is used to analyze the air leakage in goaf between the surface borehole of 8202 working face and 8201 working face. The test shows that when 8201 working face is pushed to 70 m, the protective coal pillar (38 m) in 8202 working face has been fractured, and the two adjacent goaf areas have been connected, the 8202 goaf is connected with two adjacent goaf areas of the 8201 working face, and gas exchange takes place. Moreover, the 8202 goaf within this area has well-developed fractures and abundant air leakage channels. The gas velocity and the width of air leakage zone in the air leakage field are preliminarily determined to provide technical support for the later study of gas discharge in the overlying goaf.