The utility model discloses a pulse optical fiber amplifier which adopts a two-stage amplification structure of pre-amplification plus main amplification on the whole. The pre-amplification stage adopts a highly doped single-mode ytterbium-doped optical fiber as a gain medium, the main amplification adopts a large core diameter double-clad ytterbium-doped optical fiber as the gain medium, and an isolation component is added between the two stages, so that the pulse optical fiber amplifier can work at lower repetition frequency (hertz magnitude) and amplify the pulse at the peak power watt scale to the kilowatt-scale pulse. The amplifier is relatively special in structure and can be used for research in the low repetition frequency high-power pulse amplification field.