The groundstate degeneracy of quantum spin system is a characteristic of non-trivial topology, when it is gapped and robust against disordered perturbation. The corresponding quantum phase transition (QPT) is usually driven by a real parameter. We study a non-Hermitian Ising chain with two transverse fields, one real another imaginary, based on the exact solution and numerical simulation. We show that topological degeneracy still exists, and can be obtained by an imaginary transverse field from a topologically trivial phase of a Hermitian system. The topological degeneracy is robust against random imaginary field, and therefore expected to be immune to disordered dissipation from the spontaneous decay in experiment. The underlying mechanism is the nonlocal symmetry, which emerges only in thermodynamic limit and unifies two categories of QPTs in quantum spin system, rooted from topological order and symmetry breaking, respectively.