In this paper, based on the dual-channel polarization shift-keying (PolSK) optical transmission system in which two cascaded semiconductor optical amplifiers (SOAs) are employed; the cross-polarization modulation (XPolM) characteristics of the system were studied using different code types, bit rates and time delays for the two data streams. The simulation results showed that the two polarization multiplexed channels of the system are completely independent, which can be used to transmit two data streams simultaneously with different code types, bit-rates and clock signals. Also the results showed that the system has good performances in the polarization multiplexing and de-multiplexing of the data, which are well agreed with those in our previous experimental system. Through the simulation, it was observed that the polarization-modulated signals at high bit-rate have complicated data pattern dependences and complicated optical frequency chirps which are resulted from the time varying of the phases of the optical signals.