Flow velocity estimation is an important feature in ultrasound imaging. However, in conventional color Doppler imaging, only parallel flow components can be estimated, the velocity information is not simultaneously measured throughout the region of interest (ROI) due to sequential firing of the ultrasound beams, and the size of the ROI is limited under frame rate concerns. On the other hand, ultrafast imaging is based on plane wave excitation, and the Fourier imaging method estimates the whole complex object function from k-space instead of the spatial delay and sum approach. Our goal is to derive the velocity vectors from the phase changes in the object function for ultrafast imaging.