In view of the problem of the inter-carrier interference (ICI) found in OFDM system, a proposal has thus been made of sub-carriers closure combined with time-domain windowing, followed by a simulation comparison between the power spectral density, constellation diagram and bit error curves of three different methods of closed sub-carriers, time-domain windowing and sub-carrier closure combined time-domain windowing. The simulation results show that the closure of the corresponding band sub-carriers and the selection of the appropriate window function and the roll-off factors help to reduce the external energy radiation of transmission signals, speed up the sidelobe attenuation of the power spectral density, decrease the mutual interference between carriers, effectively reduce the sensitivity of OFDM to frequency offset, and improve the BER performance of the system.