Here we report a detailed theoretical study of the mechanism of Cu+-catalyzed domino rearrangement of 2-methyl-N-methoxyaniline with a deep understanding of the unique motivation and selectivity of these migrations. We find that the Cu+ catalyst accelerates the [1,3]-methoxy migration to the methyl-bound ortho position of umpolung phenyl. The following domino transfer prefers methyl [1,2]-migration, and the rate-determining step for the whole reaction is the transfer of a proton from the phenyl ring to amine to finish the catalytic cycle.