In this study, we design a high-magnification solid-state picosecond pulse laser amplifier in which the gain medium is Nd:YAG slab. We achieve the five-pass amplification of the picosecond pulse laser through the slab multi-angle magnification technology. The seed source works in pulse mode, and the amplifier pump works in continuous mode. Picosecond fiber laser can work at different repetition rates with 13.4 ps pulse duration. After the seed laser passes through the isolation and coupling system, the single-pulse energy injected into the slab is 25 nJ. When repetition frequency of the seed source is 24.46 MHz, the output power is 377 W, the single-pulse energy is 15.5 μJ. When repetition frequency of the seed source is 49.8 kHz, a laser output power of 89 W is obtained with single-pulse energy 1.8 mJ and peak power 134 MW. The magnification is up to 7.2×10⁴.