Abstract: Coal bed joints are a widespread structure in coal beds. They are important objective in study of shaft structure and also a very important engineering geological factor . Coal bed joints affect the fabric ,structure and physical properties of coal beds,and hence affect coal bed digging and stripping,engineering character of roof,gas migration and the engineering geological conditions of coal bed methane pooling,migration,and exploitation. Studying and understanding the geometric and mechanical properties of coal bed joints make us to reasonably lay out tunnel engineering,select digging technology and to take adoption of safe measures and formulate option of coal bed methane exploitation.