At present, there is no fixed uniform standard for the size of anti-seepage curtain in various hydraulic design criteria as well as engineering practices. On the premise of keeping the seepage stable and conforming the seepage flow control standards, and based on seepage control principle, this paper presents the equilibrium seepage control method to optimize the structure of anti-seepage curtain in the order of depth, length and thickness. First, this method provides the depth of anti-seepage curtain by taking seepage quantity and slope as the standard, and then determines the length when the maximum bypass seepage velocity on two sides is equal to that in the formation of upstream and downstream of anti-seepage curtain. Finally, the method regulates the thickness when the maximum seepage velocity through anti-seepage curtain is equal to the maximum bypass seepage velocity in the formation of upstream and downstream of anti-seepage curtain. This optimal design not only ensures the best impervious effects, but also reduces financial costs. Overall, the optimized calculation results of engineering examples show that the proposed method is simple in terms of computation process and the results are reliable.