The distension of the vessel wall, which is the variation of a vessel diameter due to the distending blood pressure during a cardiac cycle, is used in the estimation of vessel stiffness parameters. A novel approach based on the empirical mode decomposition (EMD) and the Hilbert spectrum (HS) to estimate the arterial moving velocities from continuous quadrature Doppler signals is proposed in this paper. By using this approach, the high frequency blood flow components are firstly removed by using a low pass filter. Then the bi-directional signals are separated by using the phasing-filter technique. Each unidirectional signal is decomposed into intrinsic mode functions (IMFs) by using the EMD, and then the relevant IMFs from the wall are identified. Finally, the maximum velocity waveforms are extracted from the bi-directional Hilbert spectra. Results from simulation study show that this approach is practical for extracting the maximum velocities of the moving vessel wall correctly.