Base on physical amplification models established to describe the broadband laser pulse amplification processes, using numerical simulation methods, we analyse the amplification abilities of the Nd:glass laser system under different spectral linewidths. The results indicate that the output energies decrease with the increasing spectral linewidth. Compared with narrowband laser pulse of 3000 J/1ns, under the same conditions, the output energies of broadband laser pulse will reduce 2%, 11% and 27% for 2nm, 5nm and 10nm laser pulses,respectively. The influences of cross relaxation on the amplification processes are also studied. The output energies of completely nonhomogeneous broadening will reduce about 20% compared with that of completely homogeneous broadening. Then, the range of cross relaxation time is estimated to be 0—10 ns.