The invention discloses a multifrequency 
phased array ultrasonic Doppler flow detection 
system and a multifrequency 
phased array ultrasonic Doppler flow detection method. The 
system comprises a central control processor, a 
frequency synthesizer, a transmitting part, a receiving part and a display, wherein the transmitting part comprises a 
transmitter, a power distribution network, a 
beam control network, a first beam subarray and a second beam subarray; the receiving part comprises a first beam 
receiver, a second beam 
receiver, a multi-beam forming network and a 
signal processor. The 
system is characterized in that the central control processor is respectively connected with the 
frequency synthesizer, the 
transmitter, the power distribution network, the 
beam control network, the first beam 
receiver, the second beam receiver, the multi-beam forming network and the 
signal processor. In the detection method of the system, beam deflection and dynamic focusing are realized through the 
phased array technology, multi-directional and multi-depth positions can be measured on the cross section of an integral pipeline, and by a mode of adjusting 
beam scanning dynamically, the 
processing timeof the 
beam scanning is reduced, and the measuring accuracy is improved.