ω-Transaminase catalyzes the asymmetric reductive amination of carbonyl compounds, and has great application prospect in the preparation of chiral amines. The application in synthesis of bulky chiral amines is limited by the special structure of substrate binding region in the wild-type enzyme. Moreover, there are also some drawbacks in the stereoselectivity and stability of ω-transaminase. So far, -tωransaminase satisfying the industrial requirements is still rare. In this review, we first introduce the structure and catalytic mechanism of ω-transaminase, and then discuss the structural differences between S-selective and R-selective enzymes. Molecular modification of ω-transaminase was introduced in detail, by focusing on the structure and mechanism-based molecular modification, including substrate specificity, stereoselectivity, and stability.