Abstract: At present, the miter gate in lower head of Datengxia ship lock is the largest one in the world, which has three-layer prestressed back-tier rods, and the structure and stress deformation are very complicated. In order to reasonably determine the prestress of the back-tie rods, on the basis of summarizing the torsional deformation characteristics of the gate, the lateral displacement of the lower corner of the inclined joint column was proposed as the objective function to establish the prestress optimization model. By calculating and comparing with other optimization models, it was found that the lateral displacement solved by this model is obviously smaller, which indicated that the more reasonable prestress of back-tier rods can be obtained by the optimization model by taking the lateral displacement of the lower corner of inclined column as the objective function.