The branched deformations of immersed compact special Lagrangian submanifolds are studied in this paper. If there exists a nondegenerate Z2 harmonic 1-form over a special Lagrangian submanifold L, we construct a family of immersed special Lagrangian submanifolds Lt, that are diffeomorphic to a branched covering of L and Lt convergence to 2L as current. This answers a question suggested by Donaldson [8]. Combining with the work of [1], we obtain constraints for the existence of nondegenerate Z2 harmonic 1-forms.