The rotary power head is the most important part of the cutting drill. After researching the status of the rotary power head, we invented a new decelerator—roulette curve profile movable tooth transmission, and applied it in cutting drill, we presented the rotary power head with roulette curve profile movable tooth transmission. The moving components, such as the input shaft and the output shaft, of the roulette curve profile movable tooth transmission are self-balance, so the transmission can bring about random tooth number difference. Analyzing the principle of the transmission, we create the three-dimensional modeling by using Solidworks2010. The rotary power head with the new transmission installed is convenient in assembling and disassembling, transferring bigger torque, having a relatively small radial dimension, suitable for heavy-loaded rock drill machine.