Metastable α?-phase U-Nb shape memory alloys exhibit outstanding corrosion resistance and mechanical property, in which multi-level twinning martensite is the typical microstructure. Phase-field method was used to simulate the formation process of α? thermoelastic martensite. Results show that driven by minimization of elastic strain energy, various self-accommodated martensite clusters are obtained, and several self-accommodation modes are found. Comparing the simulated results with experimental results, it is suggested that the asymmetric deformation gradient tensor and interface compatibility notably influence the variant pair and twinning plane. In addition, the texture development upon deformation was predicted based on the variant rearrangement process.