For the solid-liquid two-phase flow in dredging engineering, the flow velocity of solid-phase objects is a crucial parameter to evaluate the dredging yields. However, the current computation method for flow velocity based on electrical resistance tomography (ERT) cannot effectively provide the parameter because only averaging velocity is available in practice. To address this issue, a dispersed-phase fraction-based method is proposed to separately calculate the flow velocity of not only solid-phase but also liquid-phase objects. This method first separates the solid and liquid phases from the reconstructed image using the calculated solid-phase fraction. Then, after comparing two ERT image series from adjacent upstream and downstream, the cross-correlation principle is used to calculate the flow velocity for the separated solid-phase and liquid-phase objects, respectively. Finally, Experiments based on the actual measurements in dredging engineering validate the rationality and effectiveness of the proposed method.