The electrical capacitance tomography(ECT) sensor model used in oilair lubrication testing system was set up.The capacitance values and sensitivity matrix about ECT testing of annular flow piped in oilair lubrication were solved by COMSOL Multiphysics.Taking overall score (OS) of the reconstructed image fidelity as the optimum object function,the orthogonal experiments were designed using DesignExpert to optimize the structure parameters of sensors.The results show that the order of influence degree of a single factor on OS value is that the normalized value of insulated pipe wall thickness lists at the top,the plate angle of the sensors follows,and the last one is the normalized value of the distance between the shielding layer and insulating pipe wall.Image reconstruction results show that the quality of the image is improved using the optimized sensor.