The strong optical emission of the Crab pulsar allows us to study the polarization properties in detail. Optical pulsed emission can best be understood as synchrotron radiation of relativistic electron-positron pairs in the outer magnetosphere. We calculate the polarization properties of the optical pulses based on the outer gap model, which has explained much of the observed properties of this pulsar. We find that the calculated polarization profiles exhibit the same qualitative behaviors as the observations for a large range in parameter space. It seems that the optical polarizations do not constrain strongly on the Crab pulsar's emission geometry.