A novel scheme of radio-over-fiber system to generate frequency-quadrupled optical millimeter-wave by using an external modulator and a fiber Bragg grating (FBG) filter is proposed and experimentally demonstrated. In the central station (CS), the data signal and radio frequency (RF) signal are mixed to drive the optical external modulator. We adjust the direct current (DC) bias to generate signals whose odd-order optical sidebands are suppressed. A FBG filter is employed to suppress the carrier signals, and the second-order sideband modes are transmitted to the base station (BS) in fiber. In BS, two second-order sidebands beat to generate optical millimeter-wave with quadruple frequency in the 60 GHz photodiode. The experimental results show that the 40 GHz optical millimeter-wave is generated by 10 GHz RF resource. The millimeter-wave eye diagram and the demodulated baseband eye diagram show good performance and the power penalty is less than 1 dB. The eye diagrams and power penalty result prove that 2.5 Gbit/s downstream signal can be transmitted over 40-km along fiber.