Effects of birefringent dispersion on the capability of a liquid crystal Variable Optical Attenuator（VOA） are analyzed by the Jones matrix method.The results indicate that birefringent dispersion greatly weakens its attenuating capability when working on lasers with narrow linewidths.But when it works on lasers with wider linewidths

the effects are negligible

but inevitably accompanied with a fading attenuating capability.Therefore

it is appropriate that liquid crystal VOA work on lasers with narrow linewidths and that full consideration be given to the effects of birefringent dispersion on VOA attenuating capability in its design and application.