In addition to elastic strain, the measured strain of concrete also includes non-stress strains such as free deformation, creep and temperature strain of concrete, and the methods and steps of indirect stress measurement in continuous rigid bridges of prestressed concrete are introduced. In the conversion of measured strain and stress in concrete, the non-stress gauge is used to remove the non-stress strain, the strain gauge embedded in the neutral axis of the main beam is used to identify the creep coefficient of concrete, and the creep strain is separated by the superposition method. The key to the internal stress measurement of concrete lies in the stress-strain conversion, and the key to stress-strain conversion lies in the identification of the creep coefficient. During the construction monitoring of Xijiang Bridge, the neutral axial stress was used to identify the creep coefficient, and then the creep-strain separation method was carried out, and the measured value of stress was close to the calculated value of elastic theory.