Abstract: The excitation signal of high voltage excitation electrical capacitance tomography (ECT) is about several hundreds of peak-to-peak volts, compared with normal ECT system in which the excitation voltage is only 20 V. The high AC voltage excitation ECT system has higher resolution and sensitivity of low capacitance measurement, and this will cause some new problems in designing its sensor array. The paper discussed the impact of electrode length and span on some important evaluation objects of a sensor array, and then evaluated the special image errors (SIE) of reconstructed images of core phantom, stratified phantom and annular phantom, which were under different electrode lengths and spans.Finally, a set of parameters of electrode length and span were chosen according to the simulation results.A sensor array for testing was fabricated according to the parameters. The image reconstruction results of grain distribution show that high quality images can be reached by the sensor array, this optimal design method of ECT sensor is feasible, and the parameters are also credible.