The computer simulation method of GARS spectrum is discussed in detail. The effect of laser linewidth is taken into account by convolution. This method has been used to simulate the nitrogen (N2) GABS spectra at different temperatures. With the laser linewidth used in our CABS experiment, the computer simulated N2 GABS spectra are in good agreement with the experimental ones. The approximations used in the derivation of the equations and in the theoretical calculations are also discussed.