The OFDM system has a very good performance on antimultipath. We illustrate the principle of antimultipath and analyze the impact of the multipath channel on an OFDM signal spectrum in two cases. Then we discuss the algorithms to reduce it. In a two-path channel, we simulate the OFDM system based on HiperLAN Type2 PHY protocol and analyze its performance. In the end, we offere some proposals for improving the performance of the system.