Hard milling is one of the main green machining processes, and it has become a research hotpoint. In order to monitoring hard milling process, a signal acquisition system was built. Vibration signals and AE signals were sampled in mold steel milling process. Analysis of sampled signals was conducted through time domain and frequency domain. The research shows that the time domain waveforms are different between vibration signals and AE signals in milling process; higher cutting speed results in bigger RMS values, feed per tooth and cutting depth have less effect on vibration and AE signals; higher cutting speed results in increase of amplitude in all frequency bands of vibration signals; higher cutting speed results in increase of component of frequency, which results in increase of RMS values.