With the development of information technology，it requires more power for the capacity，bandwidth，security and flexibility of the communication system.However，the communication network today gradually can’t meet this need，so the radio over fiber system has become a research hotspot at home and abroad.Through theoretical modeling，two RF signals are modulated respectively by using the two parallel Mach-Zehnder Modulators on the transmitting side of the radio over fiber system.After a long-distance optical fiber transmission，the signals are detected by using two photodetectors to on the receiving end.The two high quality beams of millimeter wave signals are produced by simulating.In the meanwhile，the eye diagram of the demodulation baseband signal is obtained.