Abstract: This paper theoretically investigates the lasing characteristics of the Rhodamine 800and DDI.Taking into consideration the temporal and spatial dependence,we get the numericalsolution to the rate eqations for some practical situation.The results show the dependence of theASE output flux upon the pumping rate and the effect of gain saturation. In addition,we alsoanalyze the gain of the system as the function of the input signal and pumping rate for the laseramplification system at 745nm.