he authors have made an all-round, systematical study on the adaptability of the A. C. drive system, which consists of asynchronous electrical motor and frequency converter to the geological drill in the case of modelling rotation and hoisting. The experiment results indicate that the A. C. drive system provides a wide speed adjusting range, good drive performance, frequent starting under load; and many optional functions such as control of max. torque, setting up of speed-increasing or reducing time. It also has high performance reliability and high efficiency. Used with drill, it can simplify the drive device of the drilling rig, facilitate optimum and safety drilling; ease automization of the drilling equipment. Therefore, application of the A. C. drive on drillrig provides a good prospect, and is a major subject worthy of further study.