A directional fracture grouting method with polymer for seepage control of dikes and dams includes the steps of: arranging a plurality of directional fracture grouting holes at a predetermined distance along the axis of the dike or dam; forming the directional fracture grouting holes by pushing a special drilling tool; placing a hole-sealing grouting pipe and a fracture grouting pipe into each of the directional fracture holes; and injecting including the steps of firstly injecting a small amount of polymer material into the sealing-hole pipe, and secondly injecting predetermined amount of material into the fracture grouting pipe. Under the chemical reaction, the mixed material expands, fractures the soil along the guided directions, and forms a super thin polymer segment. Finally, the polymer segments are overlapped each other, and the seepage control system is constructed inside the dike or dam.