The embodiment of the invention relates to a rare earth ore leaching agent. The rare earth ore leaching agent comprises ammonium thiosulfate, ammonium sulfate and ammonium chloride. Rare earth ions are exchanged and desorbed through NH4+ in the three kinds of ammonium salt; through the positive synergistic effect of the ammonium thiosulfate, the ammonium sulfate and the ammonium chloride, the rare earth ore leaching agent in the embodiment can improve the rare earth ion leaching efficiency and reduce the content of aluminum and iron impurity ions in leaching liquid; and in addition, the agent cost is low, and the rare earth ore leaching agent can be used for the development and utilization of semi-weathering ionic adsorption type rare earth ore. A rare earth leaching process in the embodiment is simple, the high leaching rate and the high selective leaching of the rare earth ions can be achieved, and the rare earth ore leaching agent and leaching process are suitable for industrial large-scale use.