Abstract: The seepage barrier composed of cohesive soil is susceptible to local non-through or vertical through-cracks as a result of the arching effect and the uneven settlement. These cracks may trigger concentrated seepage erosion, thereby posing a threat to the safety of the dam structure. Remolded clay is adopted as the test material, with pre-fabricates vertical non-through and through cracks to simulate the cracking development of the dam core. The RST-300 multifunctional seepage piping test instrument is employed to investigate the influence of crack location, crack width, and filter gradation on the seepage deformation of the clay core. The seepage discharge, pore pressure, and turbidity of the seepage water are concurrently monitored to ascertain the self-healing or erosion-induced failure state of the cracks. Results indicate that under appropriate filter gradation conditions, non-through cracks with width ≤3 mm can self-heal through particle deposition within the crack, and the self-healing characteristics are associated with the relative position of the crack and the crack-free soil. Through cracks with width ≤3 mm are capable of self-healing, whereas those > 3 mm exhibit failure modes controlled by the filter gradation and are prone to layer-by-layer cracking, fork-shaped or step-shaped failure. During the seepage process in cracked clay, the critical condition for soil particles to pass through the filter varies dynamically with the hydraulic gradient, and the filter criterion needs to be transformed from a single geometric condition to a geometric-hydraulic coupling condition.