The present disclosure provides a method for optimizing a liquid injection process of ionic rare earth ore, including the following steps of: 1) testing the hydraulic properties of an ore body; 2) determining the diffusion degree of the ore body; 3) determining the spatial distribution of the rare earth grade and the impurity grade of the ore body prior to leaching; 4) determining model parameters of competitive exchange of rare earth ions and impurity ions with ammonium ions; 5) obtaining distribution of rare earth ion concentration within the ore body after completion of leaching; 6) obtaining a profile plot of a rare earth leaching rate as a function of the concentration and dosage of an injected leaching agent; and 7) determining a minimum leaching agent dosage to achieve a target leaching rate according to the profile plot, and then determining the ammonium sulfate concentration according to the minimum leaching agent dosage.