For thorough research of contact scouring and filling protection problems for concrete cushion layer cracks in clay core dam in terms of the practical engineering, the contact seepage test method of concrete cushion layer cracks in the clay earth core dam was established by comparing different instrument schemes and by improvements of experimental apparatus and test methods. The influence factors of concrete cushion layer cracks on dam impermeability were discussed according to the seepage charactersitics tests with different conditions. After the test data analysis, the following conclusions were drawn: as to the effects of crack width, the concrete cracks of cushion layer and corridor under the filter layer should be less than 1.0mm, the cracks over 1.0mm should be properly treated; Effects of compressive stress. When the stress reached 0.5MPa or larger, compressive stress can delay the occurrence of contact scouring destruction under filter layer's protection; Effects and influences of filter layer measures. The clay particles which entered the cracks from the percolated water slowed down gradually due to the protective effects of the downstream filter layer and filled the crack.