This invention relates to crosstalk coefficient estimating apparatus and crosstalk coefficient estimating method. The crosstalk coefficient estimating apparatus is used to estimate a crosstalk coefficient of crosstalk inflicted on one channel of an optical fiber transmission system comprising two or more channels. The crosstalk coefficient estimating apparatus comprises a complex conjugate unit, for obtaining a complex conjugate signal for signal in one polarization-state of another channel other than said one channel; a multiplying unit, for multiplying the complex conjugate signal obtained by the complex conjugate unit with signal in another polarization-state of the another channel; and a filter, for filtering the multiplication result of the multiplying unit to obtain a crosstalk coefficient of crosstalk inflicted on the signal in one polarization-state of said one channel, wherein a transmission function of the filter is set according to system parameters of the optical fiber transmission system.