This paper presents a novel Radio-over-Fiber（ROF） system scheme for carrying services with different transmission rates in a single channel.Double sideband modulation is realized by using external modulators and the sidebands and carrier are separated by grating filters.The two sidebands carry two kinds of services with different rates of 1.25 and 1.5 Gbit/s respectively in intensity modulation.Simulation results show that the system performances are good after the signals are transmitted for 50 km in an optical fiber.This scheme can improve the bandwidth utilization ratio of single channels and enhance the system flexibility.