Abstract: The phonon amplification effect occurring in a single-walled nanotube was discussed, and the change rates of phonon population at different temperatures were calculated by using a time-dependent-perturbation method. It is shown that the optical phonon population increases nonlinearly with increasing laser field and the rate decreases as the temperature increases. At a definite temperature, the more intense the laser field is, the more remarkable the phonon amplification effect is, and a reasonable interpretation on this phenomenon was presented.