Molecular dynamics simulations are utilized to study the deformation process in NiAl under uniaxial tension using embedded atom method （EAM） interatomic potential. Both the tensile stress-strain curve and the atomic configurations are analyzed. The martensitic phase transformation is observed and the initial B2 NiAl transforms to a face-centered cubic ordered phase （L10）. The investigation of atomic configuration evolution indicates that the martensitic phase transformation occurs by the propagation and annihilation of 110 twinning planes. The nucleation mechanism of stress induced martensile has also been discussed.