Abstract: Multi-branch horizontal well is a new drilling technology developed in recent years.The new technology includes under-balance drilling technology,optimum design and control technique of well path,intersection technique between horizontal well and cave well,and making cave technique in coal layer.The technical specifications of the multi-branch well in coal-bed methane(CBM) field,the principles of making cave technique,under-balance drilling techniques and intersection technique were discussed.The design theory and method of well path and well structure were described.The mechanism of multi-branch well in coal-bed methane field was integrated to develop a set of theories and methods for design of multi-branch well and development of coal-bed methane.