Abstract: The influence of spectrum characteristics on diode pumped alkali laser has been studied based on the rate equations. The result shows that, there exists an optimal operation temperature for alkali lasers, and the influences of temperature and gain medium length are equivalent, thus an efficiency, independent of temperature and length, can be introduced to describe the optimal efficiency when other parameters are fixed. The influence of pump linewidth on threshold pump intensity is linear, and a high efficiency may be achieved even when the pump linewidth is much broader than the atomic absorption linewidth because of the large absorption cross section in the far wings of alkali atoms. The influence of atomic absorption linewidth on threshold pump intensity is nonlinear, and as the absorpti