Dispersive clay is a special soil which can be washed out by water easily. With the development of earth and rockfill dam, the range of choosing core material expands correspondingly. Dispersive clay as core material and its seepage-proofing effect under the protection of filters are issues concerned in engineering design. In this research we collected core materials from two stock grounds of a hydro-junction and conducted laboratory tests using pinhole, fragment, pore water solution and double areometers to determine the dispersibility of core material. By mixing different ratios of cement or quick lime, we modified the dispersibility of the core materials and compared their permeability and filter protection effect before and after modification. Results reveal that by mixing 3% of cement or 3%-5% of quick lime we can eliminate the dispersibility of the core materials from the two sites. Moreover, core material modified by cement or quick lime could bear higher hydraulic gradient than non-modified material does. Under the protection of proper filtration material, dispersive clay could bear high gradient, and has good self-healing ability in the presence of fissures.