In this paper, we study the effect of polarization mismatch (POM) in micro/millimeter-wave (mm-wave) generation employing optical self-heterodyning technology. The calculation formula of POM-induced mm-wave power penalty is derived for the first time. Utilizing a mm-wave generator based on a homemade dual-wavelength polarization maintaining fiber grating laster, several-mm-wave with frequency around 30 GHz is generated. The experimental results accord well with the theoretical ones, which can prove that the theoretical analysis is correct. Finally the simulation of effect of POM on 60 GHz is performed. Under different conditions, the bit error rates (BERs) and the eye diagrams are obtained. BER below 10-9 and clear eye diagrams can be obtained if the POM is under control. So it is very important to control the POM in fiber-optic wireless link.