This paper introduces the calculation and analysis of asymmetrical large-span box girders and the design measures taken, and takes certain design measures to solve the problems of unbalanced force and structural layout difficulties of box girders under the condition that the edge-to-mid-span ratio is extremely uncoordinated, and the design methods of asymmetrical continuous girder bridges is developed in this paper. The mechancial analysis of the box girder is carried out, and the theoretical calculation results are compared with under different cases, and the results show that the structure of the box girder is reasonable and the force is greatly improved, which provides a reference for similar structural design.