By using the Pulse-sequence model, changes in Pulse profiles and fluence of laser heams of arbitrary spatial and temporal profiles after passing through a pulsed-laser amplifier with an arbitrary gain distribution have been studied in detail. Moreover, numerical calculations have been performed and compared for two cases: (1) the losses can be substituted approximately by a total loss factor T, and (2) the medium is divided into a series of thin slabs with certain gain distributions and loss factors Ti(T=ⅡiTi). As a result, the condition of the total-loss-factor approximation has been given.