Recent experiment  revealed many new characteristics of the domain patterns in a superelastic polycrystalline NiTi tube during tensile loading, such as domain wall instability and branching, dynamic topology transition of domain patterns. In this paper, we use the continuum mechanics approach and model the polycrystal as a phase-transformable continuum described by non-local nonlinear elasticity . We simulate the equilibrium macroscopic domain patterns and their evolution in the tubes under tensile loading by the nonlocal Finite Element Method (FEM). It is revealed that the loading path dependence and dynamic topology transition of domain patterns are mainly due to thermodynamic metastability of the tube system. Our simulations capture all the key features of the domain patterns observed in the NiTi polycrystalline tubes.