Multi-pass amplification beam path alignment is based on cavity mirror alignment. To optimize multi-segmental parallel cavity mirror alignment algorithm of high power solid-state lasers, a new algorithm of multi-pass beam path cavity mirror alignment based on diffraction symmetry is proposed, and the algorithm avoids the problem of low alignment accuracy caused by image quality. The accuracy of multi-pass amplification beam path alignment is improved from 8 μrad up to 3.96 μrad. It has been verified on SG-Ⅲ facility.