Abstract: The permeability of ionic rare earth ore has a significant impact on leaching process and slope stability changes caused by leaching. Therefore, the indoor column leaching tests are used to study variation of rare earth ion permeability in percolation process. By comparing the permeability variation of ore and screening sample, the mechanism of permeability variation in leaching is explored . The results show that in water percolation process, micro-particles migration increases the seepage stability time and the range of seepage. With the increase of hydraulic gradient , the seepage field stable time decreases and flow range ability increases. In the process of leaching, the ion adsorption and the ion exchange reduces the permeability coefficient, micro-particles migrate increases the permeability coefficient,and two opposite effects coexist. When the hydraulic gradient is less than a critical value, Ion adsorption and ion exchange is the main reason changes permeability coefficient. When the hydraulic gradient is more than a critical value,micro-particles migration is the main reason changes permeability coefficient. The impact of micro-particles migration on permeability coefficient increases with increasing of hydraulic gradient. As ore's particle size distribution is dispersed and graded better,the seepage filed of ore has longer stable time than screening sample.