Abstract: Based on the transfer matrix method,the effects of the pump optical power,the distributed Bragger reflector(DBR) periods and the intensity of the input optical signal on the optical bandwidth characteristics of vertical cavity semiconductor optical amplifiers(VCSOAs) are simulated numerically.The computer model includes the longitudinal distribution of carrier and optical intensity and the influence of the ununiformity of the refractive index of the material inside the cavity on the propagation of the optical signal.The obtained results agree well with the conclusion of previous literatures.The results show that the enhancement of the pump level will increase the peak gain of VCSOAs and decrease the optical bandwidth simultaneously;reducing the DBR periods will induce larger optical gain bandwidth product.In addition,the intensity of input optical signal will obviously affect the range of the optical bandwidth of VCSOAs.