Abstract: The RRR300 superconducting niobium plate is the main material for making superconducting cavities. In order to reduce the resistance when making superconducting cavities, it is necessary to anneal the superconducting niobium plate to improve its plasticity. In the study, RRR300 superconducting niobium plate is annealed at different annealing temperatures, and the changes of microstructure, mechanical properties and RRR of RRR300 superconducting niobium plate annealed are observed.Resultsshow that 600 ℃ is the crystallization transition temperature of RRR300 superconducting niobium plate, and that 750 ℃is the ideal treatment temperature, at which temperature, microstructure, mechanical properties and RRR can reach an ideal state.