Abstract: With the increase of traffic volumn and the improvement of load grade,the issue of old bridge reinforcement becomes more prominent.In order to study the structural performance of large-span rigid frame bridges strengthened by external prestressing tendons and the spatial stress distribution of anchor blocks,the finite element program ANSYS is used to analyzed respectively the load bearing capacity of the strengthened continuous rigid frame bridge with the main span of 160 m and the spatial stresses of side-span anchor block.The results show that external prestressing can enhance the carrying capacity effectively and improve structural performance significantly,and large-span continuous rigid frame bridge strengthened by external prestressing tendons is effective and practicable;meanwhile,it is pointed out that the principal tensile stresses of the box girder at anchorage zone are existing in the box girder edge and the crossover port edge are also described.The results can provide a reference for the reinforcement of similar bridges.