The invention provides a device and method for processing a digital signal. The device comprises a coding unit, a processing unit and a mapping unit, wherein the coding unit is used for generating a first code word with a code length of M according to a code element sequence and generating a second code word with a code length of 4N according to the coding rate, a generated matrix and the first code word; the processing unit is used for performing interleaving and/or negation processing for the second code word to generate a third code word; and the mapping unit is used for mapping the third code word with the code length of 4N to N symbols to ensure that the sum of Stokes vectors of the N symbols is 0, the i-th symbol in the N symbols includes an I-way component Ixi and a Q-way component Qxi in an X polarization direction as well as an I-way component Iyi and a Q-way component Qyi in a Y polarization direction, the X polarization direction is orthogonal to the Y polarization direction, and the I way and the Q way are two orthogonal components of the same polarization direction. Thereby, the nonlinear effect of optical fibers can be eliminated by processing the digital signal.