Abstract:The development of rotary drill has experienced a course of hardly pioneering work. Proceeding from solving the problem of hole deviation, the science and technical workers has made wide and deep investigations and demonstrations, and then developed model KY120 and KY170 rotary bits and their drilling strings. These drills not only meet the requirements of drilling in new largediameter longhole stoping, but also open up a new way to expanding hole from top to bottom.