The frequency chirp of the converted signal is analyzed by using the rate equation, in addition, the amplified input signal is considered. During the course of the conversion, the amount of carriers in laser cavity will be changed when signal light is injected. As a result, the frequency of the output signal light will be changed, and the chirp of frequency will occur.The results show that higher injected current can restrain the frequency chirp effectively,and higher input optical power can also do that,meanwhile,good extinction ratio is ensured.