The rock stratum drilled by a rotary drill is random distributed and complicated, so it is difficult to define the drilling process. According to this circumstance, the drillability indexes of rock for rotary drill given out in this paper are used for continuous detection of varying rock character throughout the drilling process; on the basis of this, a control model for the rotary drilling process is established. The optimal matching of shaft pressure and rotation speed can be obtained by this model. The microcomputed control system makes the drill suit to the variation of drilled rock and keep a good drilling state. In addition, this system serves the following functions, overprocessing of drilling parameters, program control of drilling process, monitoring of drilling depth and speed, recording of rock character and guiding of alignment etc..