For online monitoring micro-size drilling,a fuzzy control method based on rough set was developed to improve original control method on too many fuzzy rule numbers and complicated calculations for a high-dimensional input fuzzy system.With processing data on line by a created fuzzy system for a spindle motor's 3-phase current signal on the Matlab platform,the connotative wear state information of micro-size drill was obtained for on-line monitoring micro-size drilling process.The results show that the breakage of micro-size drill will be effectively avoided when the monitoring threshold value is 76.7.This method has important significance for reducing the cost of manufacture and improving the productivity.