We have performed the various measurements of the transformation strain with and without the different external magnetic fields on the Ni51.6Mn23.4Ga25 single crystals. A stress-free and two-way thermoelastic shape memory, with -1.15% strain (negative sign represents the shrinkage) and 6 K temperature hysteresis, has been found in the single crystal. The deformation can be enhanced up to -2.35% with a bias field 1.2 T applied along the measurement direction of the parent phase  crystallographic axial direction. Turning the field laterally applied to  and  directions of the parent phase, however, the strain was suppressed by the field of 1.2 T to 0.56% and –0.55%, respectively, a different deformation scene. Moreover, it is found that even the field of 1.2 T does not have a significant influence on the phase transition temperature and the temperature hysteresis, which indicates that the mechanism of field-enhanced strain in this material is the twin boundary motion.