An optical secure communication system based on digital chaos and polarization shift keying (PolSK) technology is proposed. Several PolSK schemes are employed, in which states of polarization are partially or totally uniform. In different cycles of the system clock, different PolSK schemes are selected in the transmitter to modulate the information according to the real-time generated digital chaotic sequences, and corresponding PolSK schemes are used in the receiver to demodulate the information according to the synchronous chaotic sequences. The pseudo-random of the digital chaotic sequences makes the PolSK modulation schemes randomly vary. When the point number of constellation is not less than 6 and number of selected PolSK schemes is not less than 4, the optional PolSK schemes exceed 1060 kinds. Therefore, the secret key space of the system is huge. Simulation is carried out with OptiSystem and Matlab softwares, and the numerical analysis is also presented. Simulation and analytical results indicate that this system works well in transmitting information and has strong anti-attack ability.