Experiments were carried out with uniaxial tension and compression of shape memory alloys (SMA), corresponding to the processes of martensitic inelasticity, the accumulation of direct transformation strains, cross hardening, stress relaxation and limited creep. Both quantitative and qualitative differences of the deformation diagrams under tension and compression have been established. To take them into account in the nonlinear model of phase-structural deformation of SMA, it is assumed that material functions depend on dimensionless parameters of the stress and strain state type.