The invention provides an ultrasonic imaging method and device for an axial flow field of fluid in a pipeline. The method comprises the following steps: distributing a plurality of ultrasonic transducers on the two cross sections at the upstream and the downstream, and detecting the axial flow field by using a tone channel network woven by the transducers; stimulating each transducer in sequence, electronically scanning and collecting ultrasonic signals transmitted by fair current and counter current of each tone channel; calculating average line flow velocity, and obtaining projection integration of the axial flow field on each tone channel; parallelly dividing the tone channels, and subdividing projection data of each tone channel group in an interval manner; using the chromatography imaging algorithm, rebuilding the axial flow field by using the subdivided projection data, and outputting and displaying the axial flow field. The device comprises a flow field detection pipe segment, an ultrasonic signal stimulation and collection module, a tone channel line flow velocity measuring module, an axial flow field reconstruction module and an output and display module. According to the device and the method provided by the invention, quick and accurate no-blind zone detection of the axial flow field on the cross sections of the pipeline can be realized, so that high-precision two-dimensional rebuilding of the axial flow field can be realized accordingly.