The invention provides a calculation method, based on a modal analysis method, of the transverse distribution coefficient of a single-box and multiple-chamber wide girder bridge. The sensitivity factor and the sensitivity level of the transverse distribution coefficient of the wide bridge are determined by universal limit element software. Heavy numerical simulation is performed through parameterized programming for analysis, a simplified calculation method applicable to the transverse distribution coefficient of the wide bridge is obtained through solid model comparison, model tests, field tests and other contrasts, convenience is brought to design of the wide bridge, the project design quality can be improved, and the calculation method plays active roles in raising the refined design level of the wide box girder bridge, guaranteeing the structural durability of the bridge, reducing bridge diseases and reasonably controlling the project cost.