DWDM systems have been evolving to huger capacity and longer transmission distance. Intra-channel nonlinearities is one of main factors which affect very long-haul DWDM system performance at bit rate above 10 Gb/s. In this paper, we present a novel scheme, half-bit alternate differential polarization shift-keying (HBA-DPOLSK), to mitigate nonlinearities effectively. Simulation result shows that nonlinear penalties in HBA-DPOLSK systems can be reduced evidently. Moreover, because of no necessity of real time polarization tracing and control, the scheme could be implemented with less cost and more feasibility.