Based on rate equations of carriers and photons, using transfering matrix method method, the gain saturation properties of semicoductor laser amplifier (SLA) are analysed theoretically. The dependences of SLA′s gain and gain saturation on the injected current density and facet reflectivity are discussed. Although the Auger process may increase saturation intensity, it decreases the internal quantum efficiency and unsaturated signal gain greatly, so it isn′t desired in SLA.