TiAl alloys with γ-TiAl and α₂-Ti₃Al dual-phase lamellar structure possess not only excellent high temperature performance but also density only about half of traditional superalloys. Such lamellar structure largely determines the mechanical properties of TiAl alloys. However, there is still a lack of understanding on the atomic structure of lamella, as well as their influence on the mechanical behaviors. For this reason, molecular dynamics with an embedded-atom potential is employed to investigate the energies of both the coherent and semi-coherent γ/α₂ interfaces. The interface coherency is found to depend on the thickness ratio of γ lamellae to α₂ lamellae, and there exists a critical lamella thickness, below/above which the interface is coherent/semi-coherent. Tensile loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of semi-coherent interface and the crack nucleation behavior varies with the thickness ratio of γ lamellae to α₂ lamellae. The plastic deformation occurs first in the γ region, forming Shockley partial dislocations and then crosses the γ/α₂ interface via slip transfer, activating stacking faults on the pyramidal plane in the α₂ region. In this process, the γ/α₂ interface provides nucleation sites for subsequent dislocations and cracks.