In order to improve the utilization rate of optical signals in radio over fiber (RoF) system,a RoF system based on two paralleled Mach-Zehnder modulators (MZM) is proposed.The two paralleled MZMs are modulated by radio frequency (RF) signal and five optical sideband signals can be generated,which are ±1^st order sidebands,±2^nd order sidebands and optical carrier.±2^nd order optical sidebands are modulated by baseband data,millimeter (mm)-wave signals with modulated data can be generated after beating by photodiode (PD),which can be emitted by aerials.+2^nd order sideband and optical carrier are used to generate the mm-wave signals without modulated data after beating by PD,this mm-wave signals can be used as the local oscillator (LO) for the demodulation of receiving end.-2^nd order optical sideband is used as the optical carrier for uplink.In the proposed scheme,the whole five optical sideband signals are fully utilized,the utilization rate of optical signals is improved.In addition,the analytical models for transmission through a dispersive medium are confirmed.Results show that such a scheme can offer a realistic solution for RoF system.