  We predict that a non-centrosymmetric material NaSnBi locates in a
three-dimensional non-trivial topological phase under ambient pressure based on
first-principle calculations. By deriving the effective model around $\Gamma$
point, we find that the topological phase transition is driven by a Rashba
spin-orbital coupling through an odd number of pairs of band touch because of a
small anisotropic gap caused by quintic dispersion terms. In contrast to
conventional topological insulators, the spin texture of surface Dirac cone is
right-handed and the surface states are strikingly different for different
surface terminations.
