A novel structure for ultra long span optical transmission systems is proposed.In the scheme,the inverse fast Fourier trans form(IFFT) is used as a way of inverse multiplexing.A 40-Gb/s(total effective capacity) system based on the proposed scheme is simulated to evaluate its performance without consideration for dispersion compensation.Simulation results indicate that the proposed system can tolerate distortion caused by chromatic dispersion effectively after long distance transmission. A novel structure for ultra long span optical transmission systems is proposed. The scheme, the inverse fast Fourier trans form (IFFT) is used as a way of inverse multiplexing. A 40-Gb / s (total effective capacity) system based on the proposed scheme is simulated to evaluate its performance without consideration for dispersion compensation. Simulation result indicates that the proposed system can tolerate distortion caused by chromatic dispersion effectively after long distance transmission.