The effect of pre-strain on the shape memory strain and recovery stress of Ni-50.4Ti (at.%) alloy has been investigated with two kinds of heat treatment by means of electrical resistance-temperature measurement and tensile-recovery technique. The results indicated that the maximum shape memory strain or recovery stress occurs at the optimum pre-strain. The shape recovery strain and recovery stress can be improved by the appropriate heat treatment due to the improvement of the critical stress for stress induced martensitic transformation. The mechanism of recovery stress was discussed in detail.