In this paper, Er photoluminescence(PL) of Er-doped a-Si:H films, prepared by rf magnetron co-sputtering with various densities of Si dangling bonds(DBs), was studied with structure modification resulting from post annealing at a temperature range of 200-500℃. It was unexpectedly found that, the intensity of the Er-PL continually increases with annealing temperature below 350℃, meanwhile the density of Si-DBs decreases up to 250℃ due to the structural relaxation but then increases up to 500℃ probably due to Si-H being broken. Since the Er3+ ion transition depends on the symmetry of the Er3+ site in the host. The increase in the Er-PL intensity against the decrease of the density of Si-DBs is probably attributed to a change in the environment of Er3+ ions during annealing.