The invention provides a self-adaptive polarization modulation method for resisting a polarization dependent loss (PDL) effect in a depolarization channel. According to the self-adaptive polarization modulation method provided by the invention, the probability distribution function of a received signal-to-noise under the influence of PDL is derived, and on the basis, the received signal-to-noise under the influence of PDL is estimated and the estimate value information is fed back to a sending end while a polarization signal is demodulated by a receiving end; the optimal modulation order transmission data is selected by the sending end according to the feedback channel state information on the premise that a polarization modulation system meets target bit error rate performance. Meanwhile, the spectrum efficiency diagram of the system is obtained by Monte-Carlo simulation; the simulation result indicates that compared with fixed order polarization modulation, the self-adaptive polarization modulation method provided by the invention is capable of adequately utilizing a depolarization channel with the polarization dependent loss (PDL) effect and increasing the spectrum efficiency of the polarization modulation system.