In the debugging process of the prestressed tie rod,the torsion deflection of miter gate that sets pontoon will change before and after the drainage.According to the structure characteristics of miter gate,it regards the diagonal pillar as approximate rigid body.Based on similar triangle law,this paper gets calculation formula of overall deflection deducted by local deflection and corrects respectively by straight and broken line fitting method.Combined with the engineering example,this paper verifies and analyzes the deformation characteristics of miter gate through ANSYS finite element software.The results show that the similar triangle law is generally applicable to miter gate’s torsion deflection control,and can provide a solution for the debugging process of the prestressed tie rod.