Abstract: In diploid organisms, allele expression imbalance（AEI） refers to the fact that two alleles inherited from the different parents at the same gene locus and their expression levels deviate significantly from the expected ratio of 1∶1, which results in discrepancies in the contribution of parental alleles to the biological functions of offspring individuals. Although hybrid offspring of domestic animals show obvious heterosis in many important traits, the current understanding of the genetic basis and molecular regulation mechanism is still very limited. In this paper, the biological mechanism and analysis methods of AEI were introduced, and the possible role of AEI in heterosis formation of domestic animals and its future research direction were discussed, aiming to provide some theoretical basis for breeding efficient mating lines of livestock and poultry.