The ultrasonic nondestructive testing signals of carbon fiber reinforced composites have the characteristics of non-stationary and low signal-to-noise ratio, and Hilbert-Huang transform has unique advantages in feature extraction of such signals. This paper introduces the basic idea and method of Hilbert-Huang transform, which decomposes ultrasonic echo signals into several intrinsic mode functions, highlights the local characteristics of signals, and then obtains Hilbert spectrogram, marginal spectrum and instantaneous energy spectrum, so as to reveal the process of simultaneous changes of signal energy in time domain and frequency domain.