A simplified multivariant model for SMA single crystals is developed. Although the new model is a simplified version, removing explicit interaction energy calculations, it considers certain aspects of martensite transformation much better. Most significantly, martensite variants tend to rapidly form large plates most of which have an invariant plane interface with the austenite and/or reach the grain boundary. Hence the formulation of the previous Multivariant model in which every variant group is embedded in the austenite phase together with numerous other inclusions is inaccurate. In the simplified model, the energy contributed by the incompatibility of inclusion to the matrix is neglected. The prediction by the new model for different uniaxial tension directions on a single CuAlNi crystal agrees excellently with the experimental results. Furthermore, the counter-intuitive results for a polycrystalline CuZnAl SMA under triaxial loading are also well captured by the simplified model. Experimental result considering in situ loading in the MTS loading frame and SEM are shown illustrating the invariant plane in a single (gamma) '1 CuAlNi crystal under uniaxial loading. These results also necessitate further microstructure mapping for phase transition and detwinning and/or reorientation of correspondence variants in SMA with an internal twinned structures.