To study the mechanism of the influence of the plastic concrete anti-seepage system on the seepage gradient of the anti-seepage wall in the earth-rock cofferdam construction of the ship lock with high head difference，including its seepage gradient，stress，strain，cofferdam filling materials，and permeability coefficient of the formation，this paper calculates and analyzes the stress and strain of the plastic concrete anti-seepage wall by finite element method in combination with the monitoring results of the earth-rock cofferdam applied in the Wan'an second-line ship lock project.The calculation analysis simulates the filling materials in different filling areas of the earth-rock cofferdam with different constitutive models.The results show that the plastic anti-seepage wall plays a good role in seepage prevention and pressure reduction，and its effect is related to the permeability coefficient of the cofferdam filling materials and the formation.The strain monitoring results show that the anti-seepage wall is mainly subjected to compressive stress at the working stage，and the compressive strain value is -247.8×10-6-0，which falls into the allowable strain range of -750×10-6-100×10-6，ensuring the safety and reliability of the anti-seepage wall during the working stage.