Due to computer performance, nowadays only parts of the structure can be executed the simulation analysis of 3D. For the prestressed structure, after took out the target segment from the original structure, the accuracy of the result is mainly depended on the boundary conditions and the accurate simulation of the tendons. This article took the 3D simulation analysis of the arch foot for an 80m tied arch bridge for example which introduced a method that could simulate the tendons precisely when performed local stress analysis and compared the results of the common method to this method. Via the contrast the rationality and advantages of the method are clear. A certain accuracy method was presented in this article when came across the similar analysis of local structure.