On the basis that a gas/liquid two-phase flow was considered as a strongly inhomogeneous medium due to the high contrast in acoustic impedance distribution, the authors analysed the inherent dependency of the incomplete tomographic projections on the distribution of bubbles in liquid when using transmission-mode (TM) ultrasound computerized tomography (UCT). A mathematical model describing the acoustic characteristics of this flow was established. A transmission-mode ultrasonic system for tomographic imaging of gas/liquid flow was designed based upon a fast binary back-projection image reconstruction algorithm. Emphasis was made on the evaluation of its performance and its application to flow regime identification. Several flow pattern models were made and the corresponding monitoring results were given. Finally, limitations and possible future implementations of the system are discussed.