Abstract: A high speed electrical resistance tomography (ERT) system was developed, in which the electrodes were excited with a bi-directional pulse current source. The main advantages of this new design included absence of polarization effect at electrodes and high speed data acquisition due to the simplified filters design. Based on the linear back projection (LBP) image reconstruction algorithm, a modified LBP(MLBP) method was developed for this ERT system. By adopting an offline iteration technique and incorporating it with the LBP, the MLBP could reconstruct images of better quality than the LBP with similar image reconstruction speed. Experimental results showed that the new ERT system had the advantages of high image reconstruction speed and good image quality. It could implement realtime measurement of two phase flow.