Measurement and control of the laser beam focus remain to be solved as a technique for laser drilling. There have been developed many methods for laser focus control, where transducers for monitoring focus are key technologies. So the development of focus control system fitted to materials and processing schedule is very important. The sound transducer based laser focus control system is proposed, which uses aural sound as a control parameter, and measures and controlls laser focus in real time on line. Through testing the technology in diamond laser drilling system and comparing it with traditional laser control, we get a satisfying result.