Aimed at the difficulties to determine Kaiser point of rock acoustic emission, wavelet packet analysis is put torward. Based on acoustic emission tests of sandstone specimens under uniaxial compression. First AE (acoustic emission) signal noise reduction method for Kaiser point using wavelet packet is presented. Then get the frequency of AE signal. Last, using the wavelet packet analysis study the energy distributions of AE signals and the characteristic frequency band of Kaiser point are obtained. Results show that wavelet packet analysis is an effective way in processing of rock AE.