Electrical capacitance tomography（ECT） is one of process tomography（PT） technique which developed rapidly and matured in recent years.Its sensitivity distribution function depend on the permittivity distribution

namely ’soft field’ characteristic of ECT sensor.The image-reconstruction algorithm is done by the sensitivity distribution of the known permittivity.According to analyze of the detection sensitivity of object measured with variable permittivity

one step simulation calculation method is used to calculate the permittivity of medium

when pipe is filled with high permittivity and low permittivity object respectively

filter linear backgroud projection（FLBP） is used to reconstruct the unknown permittivity object.