Introduction: Through the field test of the elastic modulus of different age and steam curing box girder, it is found that the elastic modulus decreases after the box girder is removed (5 days), which provides a basis for optimizing the tension/release time of the structure. Through the relationship between age and elastic modulus, the modulus of the box girder after 28 days can be further calculated through the low age structure, and new measures are proposed for the optimal construction of the box girder.