Abstract: For in-situ leaching of ionic rare earth ore bodies, seepage is an important controlling factor of rare earth ion leaching rate and leaching cycle and becomes the key to improving leaching efficiency. In this paper, the rare earth ore block from Zudong area (Longnan County, Ganzhou) was taken as the experimental object of column leaching. With magnesium sulfate solution as lixiviant, the effects of magnesium sulfate solution on pore structure, rare earth ion concentration and solution leaching rate of ionic rare earth ore body were studied by NMR, EDTA volumetric method and data fitting analysis, and the evolution mechanism of pore structure during in-situ leaching was discussed. The results show that the water-leaching process has little influence on the pore structure of ore body, and a small number of macropores transform into small pores. In the leaching process, the pore structure of ore body is greatly affected by magnesium sulfate solution, and the porosity first changes from macropores to small pores and then from small pores to macropores with the characteristics of hindering the lixiviant seepage, which increases with concentration. Finally, the relationships between leaching rare earth ion concentration and the average leaching rate of leaching groups with different concentrations were fitted, respectively.