A novel physical layer security scheme based on channel pre-compensation is proposed to enhance the communication security in Polarization Shift Keying (PolSK) modulated systems. By using channel pre-compensation, which is performed based on the knowledge of channel, the original signal constellation is distorted, so that only intended receiver can recover. The proposed scheme makes the estimation of the constellation difficult for the adversary. The security and efficiency performance of the proposed scheme are analyzed via simulations.