Electrical capacitance tomography is a new technique for monitoring two-phase flow. It can reconstruct cross-section phase distribution images of the pipeline through which two-phase flowruns. Due to the advantages of ECT technique such as non-invading, without environment pollution, on-line real-time measurement, low cost, reliable working and low maintenance costetc, ECT has been gradually applied in industrial production.ECT technique is based on the theories of static electric field. When the electric line of force enters another kind of medium with different dielectric constants from a kind of medium, it will deflexion in the interface. In addition, the sensitivity of static electric field relates to the density degree of the electric line of force, generally speaking the sensitivity close to the electrode pole is higher than that of the "central" part. Though the technique of ECT has its unsatisfactory aspects,but just as what is stated above, the outstanding merits of this kind of technique make it becomeone with the fastest developing speed in the method of a great deal of PT technique. It offers new visualization method for the interior characteristic of the industrial process and provides valuable information for the industrial production and evaluation of device design. ECT is a strong tool foron-line monitoring of industrial process whose development prospect is hard to assess. It is themost promising measurement technique among the process tomography methods.The basic principle of ECT technology is as follows. When the liquid in the pipeline or inthe process container is flowing, the capacitance value of the sensor on the surface of the pipeline will change accordingly. ECT sensor is composed of several pairs of metal electrodes symmetrically placed in insulating pipeline or in process container, each two different electrodes form a two ends son-capacitance pair, which corresponds with different measuring sensitivityarea. Its capacitance value is measured by data gather system. The data measured from all different pairs of electrodes reflect the distribution of dielectric constant on the cross section ofpipeline. All these data are feed back to the image-reconstructing computer to gain distribution image of object through certain image reconstructing arithmetic.In the process of electrical capacitance tomography, if the distribution of the dielectric insensors across-section is given, then to calculate the capacitance value between the electrodes isa positive deduction of the capacitance tomography. But the actual imaging is a reverse deduction,that is to get the dielectric distribution of the sensors across-section according to the capacitancevalue between the electrode pairs. The positive deduction is the important base of the reverse deduction. In the positive deduction, to get the sensitivity distribution of the tomography system is the precondition of reconstructing the image. The sensitivity field of the tomography system isaffected by the medium distribution of multi-phase flow, which is called "soft field character"which brings many difficulties in reconstructing images. In order to improve the quality of thereconstructed image, it is necessary to analyze the sensitivity distribution. In the paper a set ofcapacitance tomography based on 12-electrodes capacitance sensor is introduced and thesensitivity field distribution of the 12-electrodes capacitance sensor is got through the self-writtensoftware.Through the actual test, the theoretical model is proved to be right, and the result is gotthrough the data measured. Because measurement of the weak capacitance is involved in thepractical measurement, so the system is required to have high sensitivity and high resistanceability. In addition, due to the "soft field characteristic" of the sensor and the limitation ofgeometry size of the pipeline, which leads to not being able to put more electrodes on thepipeline, the number of the measured independent capacitance value (projection data) is limited.All the factors above lead to the reconstructed image existing some error, so this method needs tobe improved.