Abstract: Based upon instantaneous output spectra of xenon flashlamp, a unique dynamic modeling program has been constructed to predict the gain performance of multisegment Nd: glass laser amplifiers. The model, which includes the all dynamic modulations from flashlamp discharging to laser outputting, may be used in laser amplifier system optimizations. The influences of disk thickness and Nd2O3 doping level on gain performance are studied with the modeling program. Under the condition of the same pumping lever, the stored fluence and the small signal gain are determined by the doping-thick ness products(Nd ion concentration by slab thickness)in the MAS slab.