Abstract: Prestressed tensioning is an essential link in the construction of prestressed bridge, which is of great significance to the automatic and precise control of the tensioning process and the end point. This article designed an automatic prestressed tensioning control system, on the basis of automatic checking tensile tension and tensile elongation, established the relationship between tension and elongation during construction, meanwhile, according to the construction standard, implemented the determined of the effective prestressed point, and then determined the end of tension. Under the premise that the tension elongation error is less than 0.1 mm and the tension error is less than 0.02 MPa, the test and field application showed that the accurate rate of determining the effective prestress point was 98% by using the proposed method, it could meet the requirements of automatic construction.