Abstract: Picosecond pulse laser with high average power is critical to applications such as industry processing, space exploration, etc. However, due to the narrow pulse width and low single pulse energy, the mode-locked picosecond seed light is difficult to be amplified directly through the traditional traveling-wave amplification, which limits the nonlinear frequency conversion efficiency. Here, by using grating chirped-pulse stretcher and slit, seed light pulses with a pulse duration of 7 ps and a central wavelength of 1030 nm at the repetition rate of 52 MHz were stretched to 32 ps with the spectral width of 1.1 nm. Then the average power was amplified to 190 W by using two air-clad photonic crystal fiber amplifiers (PCFAs). Finally, via a temperature phase-matched LiB₃O₅ crystal, output power up to 103.1 W was obtained with the beam quality factor 1.17 and the second harmonic conversion efficiency of 54.3%.