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.