The function of optical spectral reshaping(OSR) filter in chirp-managed modulation format and its effect on the output chirp of direct modulation laser(DML) were discussed in the paper.The types,bandwidth,center frequency,filter order and the position of the OSR in the CML system were systematically optimized.The results show that the first-order Gaussian reshaping filter with an optimized bandwidth of 8.4 GHz and center frequency of 193.1237 THz,which is at the transmitting end,has the best performance in the CML fiber transmission system without dispersion compensation,and the dispersion tolerance of 1dB eye opening penalty is 5047 ps/nm.