Abstract: The time-depended rate equation model of four-level excimer pumped alkali laser (XPAL) is established, and the population of each level and laser intensity in cavities varying with time are calculated. The result is compared with experiments, and it indicates that the threshold pump intensity of XPALs is too high. Matching the spectral width of pump to the width of absorption could not improve the absorption efficiency, neither could law down the pump threshold. When the pump intensity keeps the same, the absorption efficiency could be improved by either increasing the length of gain medium or the temperature, but the pump rate in unit volume decreases. The key to success ofXPALs is to achieve effective pump absorption.