A technique for tunable microwave/millimeter-wave generation based on a polarization-stable dual-wavelength polarization maintaining fiber Bragg grating (PMFBG) laser is proposed in which the frequency selecting of PMFBG is used to produce two polarization-stable lasing signals, the polarization scrambler is adopted to ensure the consistency of the orthogonal polarization's power, and then the beating frequency in high-speed photodetector is used to generate the microwave/millimeter-wave. Lateral strain loading on the PMFBG allows the frequency of the microwave/millimeter to be controlled. In the experiment, a scheme for tunable microwave/millimeter-wave generation based on a polarization-stable dual-wavelength PMFBG laser is produced, and the microwave signals of 20.407 GHz and 22.050 GHz are generated by different axial pulls loading on PMFBG. In the simulation, the millimeter-wave of 60 GHz is generated and transmission performance of the millimeter-wave in radio-over-fiber downlink is analyzed. The results show that the eye diagrams demodulated in the mobile station are excellent when the optical carrier which is modulated as the millimeter-wave sub-carrier transmits over 80 kilometers from center station to base station. The excellent performance of the system is verified.