The AE signals of fiber reinforced composites in the tensile testing were processed by Hilbert-Huang transform. The AE signals were well recognized from the Hilbert-Huang spectrum. The experimental results show that the frequency range of matrix crack AE signals is below 200 kHz and the main frequency is nearly in 175 kHz. The frequency range of fiber breakage is above 200 kHz and the main frequency is nearly 250 kHz. While the frequency of delaminations is distributed all over the frequency range and the energy is distributed below 200 kHz. The experimental results also indicted that the intrinsic mode function (IMF) components of the AE signals processed by empirical mode decomposition (EMD) can reconstruct the original signals well, and the Hilbert spectrum of the IMF components can reveal the frequency and energy trends of AE signals.