A method was presented for the noise analysis of a ball mill by usin g the power spectrum. By using the property that the ball mill’s noise in the med ium and high frequency bands were sensitive to the material level, the changes o f material level were analyzed and calculated. A real time condition monitor sys tem for the ball mill was constructed, which mainly consisted of an “electric e ar” sensor, a set of sound card collection device and the LabVIEW8.0 software. The application shows that the system succeeds in improving the efficiency of th e ball mill and reducing the energy consumption.