The article presents the stationary solution of the Tang–Statz–DeMars system of equations describing the generation spectrum of YAG : Nd laser at a wavelength of 1064.2 nm in terms of seven lines of amplification of the transition 4F3/2 → 4I11/2. The line broadening effect, due to temperature increase, on the generation spectrum of YAG : Nd laser has been calculated. Moreover, the effect of population distribution over the 4I11/2 multiplet sublevels on the laser generation spectrum was also calculated. The generation spectrum shift to the region of 1066 nm with temperature increase was found to result from variations in the population of the 4I11/2 multiplet sublevels.