A polarized light multi-pass amplifier based on a spliced crystal comprises a polaroid, a Faraday polarization apparatus, a first total reflective mirror, a second total reflective mirror, a third total reflective mirror, a fourth total reflective mirror, a spliced crystal, a fifth total reflective mirror, a first 1 / 2 wave plate and a second 1 / 2 wave plate. The light beam polarizing angle of a light beam of the multi-pass amplifier in a transmission and amplification process is 45 degrees, thus the spliced crystal is formed by splicing crystals whose C axes are 45 degrees, difference of polarization states of linearly polarized light is utilized, a two-pass amplifier structure is utilized to realize traditional four-pass amplification, the incident angle alpha when a seed light beam is incident to the crystal is reduced, finally, the area of a seam of the spliced crystal on a light spot projection plane is reduced, and the amplification efficiency is improved. The two 1 / 2 wave plates are placed in a pumping light path, and has no influence on the state of the seed light beam, thereby saving cost, and ensuring the reliability of the amplifier.