Water-blocking yarn is made by polyester industrial filament and cross-linked polyacrylic expanding material. It has advantages of high water absorption speed, high expansion ratio, strong tensile strength, no acid and alkali, no compatibility effect on cable, heat resistance and chemical stability, non-corrosiveness， etc. In manufacturing process of optical fiber cable, materials such as filling gel, water blocking tape, tie yarn and so on can be omitted. The water-blocking yarn is easy to use, simple in process, stable in structure, reliable in water resistance, environment friendly and does not cause oily pollution.