the vital technology of burst-mode optical transmission in the Optical Burst Switching (OBS) and Passive Optical Networks (PON) are analyzed and the design scheme of 1.25 GB/s burst-mode optical transmitter using external modulation is put forward. Its core component is the coupled apparatus of DFB LD and external absorption modulation (EAM). The method of the modulation actualizing the burst-mode optical transmitter is demonstrated and the technological indicator of burst-mode optical transmitter is summarjzed