The emission Mossbauer spectroscopy in combination with other methods was used to study NiTi shape memory alloy(SMA) after the sample was water quenched from 700℃ and aged at 500℃ and isochronal annealing at different temperatures. The Ni56Ti44 phase in NiTi SMA has been obtained after different heat treatments. The reason why the NiTi SMA has the best shape memory property after quenching from 700℃ and aging at 500℃ is also given.