The present disclosure provides an ultrafast Doppler ultrasound method for estimating a blood flow velocity through repetitive compounding of multi-angle plane waves. The method includes: controlling an ultrasonic transducer to cyclically transmit plane waves (101) according to a sequence of deflection angles of {0, −β, β, −β}; receiving echo signals (102) of the plane waves reflected by an area to be scanned; searching for three consecutive frames of signals with deflection angles in a sequence of {0, −β, β} and {β, −β, 0} in the echo signals to obtain multiple frame groups (103); compounding the three consecutive frames of signals of each frame group to obtain a compounded radio frequency (RF) signal (105); calculating a blood flow velocity (106) according to the compounded RF signal; and performing color coding on the blood flow velocity to generate a two-dimensional (2D) blood flow velocity image (107).