The main mechanism is that the water leakage channel of earth dam is separated by the impermeability of plastic film, which can bear the water pressure and adapt to the deformation of dam body with its large tensile strength and elongation; and the non-woven fabric is also a kind of short polymer fiber chemical material, which has high tensile strength and extensibility through needle punching or hot bonding. After it is combined with plastic film, it not only increases the tensile strength of plastic film Because of the rough surface of the nonwoven fabric, the friction coefficient of the contact surface is increased, which is beneficial to the stability of the composite geomembrane and the protective layer. At the same time, they have good corrosion resistance to bacteria and chemical action, are not afraid of acid, alkali and salt erosion, and have long service life under the condition of avoiding light.