Abstract: A new triaxial equipment combined with ultrasonic apparatus was developed.The structural change of samples during triaxial compression tests was measured by ultrasonic techniques.A series of tests for concrete samples were conducted and the ultrasonic data were analyzed using wavelet.Three characteristic values which could reflect damage evolution of samples were put forward in frequency range.They were the first normalization peak value of energy,the second normalization peak value of energy and the scale corresponding to the first normalization peak value of energy.These three characteristic values could reflect the inside structure change of materials.Especially,the third characteristic value had good regularity and could be used as damage variable.