Dispersion-flatten fibers are used to suppress the third-order dispersion to some extent based on the effect of third-order dispersion on pulse transmission by polarization multiplexing technique with zero dispersion wavelength. However dispersion-flatten fibers are only useful in short distance transmission. A new method is proposed to compensate the effects of the third-order dispersion by means of the cascade of many short fibers with alternate positive and negative values of the third-order dispersion. The method is proved practicable in long distance transmission by numerical simulation.