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The asymmetry associated with martensitic transformations observed in tension/compression experiments of shape-memory-alloys (SMAs) is investigated on the basis of a recently suggested micromechanical model. The approach is based on crystallographic theory and utilizes a framework of energy minimization in a finite deformation context. Polycrystalline NiTi under tension demonstrates smaller phase-transformation start-strain, different phasetransformation stress-levels and flatter phase-transformation stress-strain slopes than that under compression in our numerical simulation. The phase-transformation start-stress is followed to have a linear relationship with respect to the temperature within a certain range. These results agree well with experimental results reported in the literature.