The external prestressing system was first designed and applied in the southeast half ring viaduct project of the express road in the central city of Tianjin. Taking the construction of the bridge as the background, This paper introduces the application of external prestressing system construction technology in the project, and strives to find out the process of external prestressing construction technology and the key points of construction control, find out the role and characteristics of external prestressing through the construction of the project, and prove the feasibility of the construction technology through the detection of the stress and strain of the box beam concrete, which provides technical reserves and lays the foundation for the promotion of the technology The foundation.