Abstract: In order to estimate the maximal repeater length in long-haul repeaterless light-wave system, a new approximate method, which is used to solve Non-linear Schrodinger Equation piecewisely, is given in this paper. By this method, self phase modulation (SPM) , group velocity dispersion (GVD) as well as attenuation are considered. The whole transmission distance is treated as two segments, SPM is considered only in the former segment, while GVD is considered in the latter. Frequency chirp is the link between two segments. By which, the relation formula between distance, bandwidth and initial frequency chirp is given. Adding the optimal initial frequency chirp given by graphic method, we get the simple relationship between distance and bandwidth. The maximal repeater length of 2.5Gbps system is obtained by this method. Its validity is also proved by slip-step Fourier algorithm.