We develop a new algorithm to evaluate the thermal features of a rubidium-vapor cell and a cesium-vapor cell pumped by the laser diode. The theoretical model is based on the principles of both heat transfer and laser kinetics. The obtained population density distribution and the radial temperature distribution are analyzed for both types of cells. It is thought that the theoretical results are logically reasonable and the mathematical precision is satisfactory in designing a real diode-pumped alkali laser (DPAL). The methodology is valuable in the construction of a high-powered DPAL in the future.