A combined model of phase and structural deformation for shape-memory alloys is considered. The model takes into account kinematic and isotripic hardening and can be used for describing the phenomenon of oriented transformation. According to the model, phase deformation can increase under a decreasing load or without load after preload. Concepts of the loading surface and active process are used for structural deformation description. Structural deformation in the active process is determined by the associated law by analogy with the plasticity theory. Tensor increment of the structural deformation is required to be codirectional with the external normal to the loading surface, and the hardening parameter associated with the structural transformation correspondingly is required to be positive. The majority of models consider only formation of new martensitic meso-elements, not taking into account the development of the elements formed earlier. Meanwhile, experiments show that the development of martensitic elements can significantly influence on deformations. In the considered model, a special material function determines the relationship between the processes of formation and development of martensitic elements. The temperature of the phase transition in shape memory alloys depends on the operating stress, therefore phase transition can occur at a constant temperature. The article examines the possibilities of the combined model for describing the phenomenon of superelasticity in titanium nickelide. The nonlinear dependence of deformations on stresses and the corresponding phase-structural transformation after reaching stress thresholds is modeled. The results for different material functions are compared. Phase deformations are higher for material functions that take into account the development of martensitic elements. The model correctly describes the nonlinear growth of deformations under monotonically varying stresses at a constant temperature and the phenomenon of superelasticity. At monotonically increasing stresses at a constant temperature, the influence of the development of martensitic elements is less noticeable than at decreasing stresses.