Electrical capacitance tomography (ECT) sensor has the ‘soft field’ characteristic which means the sensitivity distribution is dependent on the permittivity distribution.To obtain high quality reconstruction images,sensitivity matrix of an ECT used in oilair lubrication testing system was solved quickly by COMSOL software.The soft field effect on the sensitivity of two typical flow patterns,laminar flow and annular flow,in the pipeline was analyzed by both COMSOL software and MATLAB software.Two flow patterns were reconstructed separately by LBP algorithm and OTSU algorithm when the soft field effect was taken into account or not.Simulation results show that the sensitivity distribution is changed when the soft field effect exists,and the detection sensitivity is higher when the lubricating oil is closer to the wall of pipe,and precision of the reconstructed image is improved effectively using the sensitivity matrix changed by the soft field effect.