In order to weaken the bit format effect of converted signal of wavelength converter based on cross-polarization-modulation in semiconductor optical amplifier (CPM-SOA), the principle of CPM-SOA wavelength converter is analyzed; and after discussing the characteristics of frequency chirping of converted signal pulses, a simple method is proposed to improve the bit format effect by using the positive or negative transmission slope of a filter to optimize the converted signal of in-phase or out-of-phase. 10 Gb/s wavelength conversion based on CPM-SOA experiment is demonstrated by using a JDS filter with 0.3 nm optical bandwidth, the bit format effect of long “1” bit and long “0” bit in converted signal is mostly eliminated, the converted signal of in-phase or out-of-phase is reshaped and their power penalties are reduced by more than 3 dB.