One of the main elements of the thermodynamic behavior of shape memory alloys (SMA) are the governing equations for the velocities of phase deformation in direct thermoelastic transformation. This paper describes the results of experimental studies on samples of NiTi, allowing you to select an adequate form the simplest version of these relations. It was established that the strain accumulated in full direct transformation under the influence of too high DC voltage increases linearly with these stresses, the sample after a certain thermomechanical training this dependence is reduced to a direct proportionality. For the strain accumulated in the direct transformation under the influence of the two-stage loading, received a kind of form of the law of linear summation of relative deformations, which was tested in the experiment. It was found that the samples are cooled under the influence of tensile stress, before the direct conversion experience compressive strain is large enough quantities, which is almost an order of magnitude possible thermal distortion.