The invention relates to a real-time simulation system based on FPGA multispeed optical fiber communication and a simulation method thereof. The real-time simulation system comprises an optical fiber signal converter having a parallel multispeed low speed interface terminal and a serial high speed interface terminal, and the parallel multispeed low speed interface terminal is connected to a communication board card or an external controller through an optical fiber; and the serial high speed interface terminal is connected to a real time simulation machine through the optical fiber; the optical fiber converter converts a multi-channel and multispeed low speed optical fiber transmission of the external controller to single channel high speed optical fiber transmission and transmission between the serial high speed interface terminal and the real-time simulation machine is transmitted to a real time simulation machine through Gbit or an Aurora protocol in order to form a dual-end loop; the FPGA samples low speed optical fiber data with high frequency to eliminate an shaking error, and realizes multiple verification functions. Various transmission speeds realize high speed conversion through RAM and are transmitted to an OP5660 real time simulation machine. The technical scheme of the multispeed optical fiber communication real time simulation system based on FPGA multispeed optical fiber communication can save resource of the simulation machine and satisfies requirements for various kinds of control board cards and increases flexibility, and expandability of the optical signal converter is strong.