To study the effect of transverse stiffness on the mechanical behavior of reinforced concrete rigid-frame arch bridge, an integral model was set up by using the spatial finite element analysis software, four different spans rigid frame arch bridges were analyzed and the influence of transverse load distribution coefficients on different deck stiffness was studied. Compared with the results of deflection method, it shows that the transverse load distribution coefficient calculated by elastically supported continuous beam method is smaller; also, the transverse stiffness is directly related to the magnitude of transverse load distribution of the bridge and a serious difference of the forces calculated with traditional design theory, which should be modified in the design.