As a key device in ASON (automatic switched optical networks), the study on all optical wavelength converters is becoming a very important project. A theoretical model of wavelength conversion based on semiconductor laser is established. The frequency modulation response of wavelength conversion is discussed by using rate equation under the small signal analysis. The characteristics of wavelength conversion are analyzed in different optical parameters including the injection current, signal average power, gain coefficient and so on. Those results are useful to optimal design of the wavelength converter based on semiconductor laser.