Abstract: Taking example for sine wave and triangle wave,this paper analyzes analog optical signal's cross phase modulation characteristics in semiconductor optical amplifier,including gain,nonlinear phase difference and chirp.Analysis shows that when using the frame synchronization between signal light and optical control pulse,the gain and gain difference at each point of signal pulse will fluctuate,the nonlinear phase difference also will deviate from the ideal value of π.In order to obtain the same nonlinear phase difference at different point of signal pulse,bit synchronization mode should be used,and the needed optical control pulse has the similar waveform to optical signal pulse.