In the semiconductor optical amplifer,based on the theory of four wave mixing effect and refractive modulation-index generated by equivalent grating,dynamic changes of the signal light time delay with the outside controllable parameters,such as the injection current into semiconductor optical amplifier(SOA),the pump light power,the detuning frequency between pump light and signal light,were numerically simulated by the method of subsections model of SOA.Compared with the former simulation of slow light from the slow down factor view,this method has the advantage of associating the signal time delay with outside controllable parameters and providing the intuitional guidce for the experiment.Meanwhile,the method by subsections model of SOA has higher accuracy.Compared with the existing experimental results,it indicates that the numerically simulated results agree well with the measurements.