A thin-disc multipass laser amplifier enables a seed laser to frequently pass through the gain medium to extract energy. Such an amplifier can output a high average power, high pulse energy, and high beam-quality laser, which plays an important role in a high power short-pulse laser system. In this paper, a Yb∶YAG thin-disc multi-pass laser amplifier that can amplify a seed laser over the course of 20 passes is designed and constructed. An amplification of a high-repetition frequency short-pulse laser is performed, and it is found that the thin-disc multi-pass laser amplifier can effectively guarantee the beam quality of the output laser. In addition, spectral mismatch is observed to have an influence on the single gain of a short-pulse laser.