Abstract: In order to meet the needs of hydraulic reverse-circulation continuous core drilling,the power head has been redesigned.The power head is driven by the two-speed alternating current motor.Matching with the gear case,four kinds of rotary speeds and wider speesd range could be obtained,so it can not only satisfy the speed requirement of bits made by different materials,but also has the properties such as simpler structure and lower cost.The hollow dual-wall pipe is used in the spindle of the power head and the water swivel is combined with the power head,so the system is more compact,Through drilling tests,the power head words well and suits the hydraulic reverse-circulation continuous core drilling.