An ultrashort pulse laser system based on ultra-large-mode-field fiber amplification is reported. The laser system adopts fiber chirped pulse amplification amplification structure. The pulses with 500 fs are stretched to 500 ps by volume Bragg grating (VBG). The seed laser with average output power of 10 mW and repetition of 40 MHz is amplified by Yb-doped fiber amplifier. The repetition is adjusted to 500 kHz through the acousto-optic modulator. Then we use the large-mode field core diameters of 40 μm and 85 μm photonic crystal fibers as power amplifiers. Finally the laser with center wavelength of 1030 nm is compressed by VBG. The average output power is 104 W, and the near-diffraction-limit 767 fs pulse with maximum peak power of 0.271 GW is achieved.