Short-haul high-speed information transmissions can be realized by applying the Orthogonal-Frequency-Division-Multiplexing(OFDM) technology to Multimode Fiber(MMF) transmission links.The mode dispersion of MMF is calculated by using the optical angular spectrum method and a theoretical model of the directly modulated MMF transmission is built on the basis of the OFDM principle and such typical system performance parameters as transmission rate and BER are numerically analyzed.The results show that the transmission distance of the standard OC-768(40 Gbit/s) signals in SONET can be as long as over 2.5 km when the receiver BER is limited to 10-3.