The field transfer matrix and point matrix are derived, and the inner force, stress and deflection of thin-walled box girder are recursivly calculated.

So it is necessary to do some further researches in thin-walled box girder, especially in multichambered thin wall box girder.

The adoption of the thin-walled box girder to the Y-shape bridge makes the restrained torsion effect, distortion effect and shear lag effect prominent.