Shape memory alloys (SMAs) are new functional material featured by the excellent properties including shape memory effect and superelasticity. NiTi SMAs have some important implications in avitation, medical device,etc. The main objective of this work is to derive a simple Taylor model for NiTi polycrystal.By the assumption of laminated microstructure and perfect interfacial relationship for NiTi single crystal transformation, microscopic strain for each phase can be transformed to overall strain of respective volume element, and expression of phase transformation driving force is derived, then control equation of phase transformation is constructed. Based on the single crystal model, the NiTi polycrystal constitutive model is constructed by Taylor assumption. The model is used to simulate the mechanical response of NiTi polycrystal alloys with strong {111} texture, the results are in agreement with those observed experimentally. The predicted result of NiTi alloy with strong texture shows asymmetry of tension and compression. Simulation results behave softening as the free energy function is non-convex during phase transformation. Transformation stress level rises as temperature is raised.