Abstract: In deducing the differential equation of the box girder contortion (distortion),^[1] we take the shear angle r(z) as the unknown and adopt the plate girder frame method to make the deduction. But the involved process of deriving the formula is comparatively lengthy and tedious. To begin with, we derive them by taking the contortion (distortion) deflection as the unknown, Then we base on the closed thin wall stanchion theory and the energy method, we converse them into the differential equation of r(z). The physical concept is clear and the deduction process is concise. Finally we get the solution of w. By making use of Steinle formula, we deduce the analytical expression of the contorted double moment.