Three typical acoustic emission signals for carbon fiber epoxy laminate in tensile damage are investigated by approximate entropy theory. The computed results show matrix cracking, debonding and fiber breaking own some different characteristics of approximate entropy spectrum which is construed by empirical mode decomposition (EMD) method. In addition, spectral distribution of intrinsic mode functions for the three kinds of acoustic emission signals is analyzed which further illustrate approximate entropy in essence is measuring the probability of new vibration mode in signal, and demonstrate the effectiveness of using approximate entropy spectrum analysis in acoustic emission detection for composite material.