The invention discloses a method and a device for improving performances of a polarization controller. The method comprises the steps as follows: the polarization state of an optical signal output by the polarization controller is monitored and a four-way voltage signal matched with the polarization state of the optical signal is output; four-way Stokes parameter signals (S0, S1, S2 and S3) of the optical signal are obtained according to the four-way voltage signal and the quadratic sum of the difference value between each sampling value of four-way Stokes parameters matched with a generated polarization control signal and the target Stokes parameters matched with each sampling value is minimum; and the generated polarization control signal is input into the polarization controller. The embodiment of the invention can reduce the influences of residual double refractions in the polarization controller and improve the performances of the polarization controller.