Abstract: The transverse load distribution for bridges with large side beams is analyzed by adding fictitious longitudinal beams. The basic formulas considering the effect of large side beams are derived and verified through a numerical example. In order to understand the characteristic of load distribution for the bridge with large side beams, the effects of stiffness ratio of the large side beam to the interior beam and interior diaphragms on the load distribution are studied in detail by means of the developed program based on the derived formulas. A large number of charts are drawn to show clearly the influence regularity. Research results show that the increase of stiffness for side beams affects remarkably the load distribution. It leads to great increase of the transverse distribution factor for side beams and reduction for internal beams. But when the stiffness ratio increases to a certain value, the degree of above-mentioned influence becomes very little. Interior diaphragms cause certain increase of transverse load distribution factor of large side beams while great reduction to internal beams.