The COMSOL software was employed to establish a threedimensional physical model of electrical capacitance tomography (ECT) sensor for an oilair lubrication system,and its mathematical model considering the capacitance of the pipeline was got .The influence factor of the pipeline capacitance was defined,and the influence of the thickness and the radius of the pipeline on the measured capacitance was analyzed.The image of the annular flow was reconstructed by using LBP algorithm and considering the pipeline capacitance,and the quality of reconstructed image was evaluated.The results show that the influence of pipeline capacitance on the measured capacitance can be represented by the influence factor of the pipeline capacitance,the effect of the pipe capacitance on the measured capacitance will increase with the increasing of pipleline thickness or the decreasing of pipeline radius,especially the pipeline capacitance has a greater impact on the measured capacitance for small diameter pipes in an oilair lubrication system.The quality of reconstructed image is improved in a certain extent when the pipeline capacitance value is taken into account in the algorithm.