Based on nonlinear theory of reinforced concrete, the influence of diaphragms' cracking on the load transverse distribution for the prestressed concrete multi-T-girder bridge is studied. Compared with results from traditional theory called hardening connective plates, the applicable range of the theory is determined. From shell element degraded from continuous body, steel and concrete are modeled by layered shell element. With some available criteria, the material nonlinear properties of concrete and steel are considered. Then the procession of cracking, yielding and failure of prestressed concrete multi-T-girder bridge is imitated and the analytical three-dimensional procedure is compiled. For a certain prestressed concrete multi-T-girder bridge, combined with traditional theory of hardening connective plates, some loadcases including uniform loads, symmetric loads and offset loads are calculated. From the results, it is shown that the cracks in the diaphragm weaken the transverse connections between the beams, which leads to the unsatisfying change of the transverse distribution of the loads. When the bridge is subjected to uniform loads, the result from the nonlinear procedure is coordinative with that from the theory of hardening connective plates. When the bridge is subjected to symmetric loads and offset loads, the result from the nonlinear procedure is not in agreement with that from the traditional theory and when the diaphragms are in cracks, analysis by the theory of hardening connective plates may lead to large error, which will produce unsafe results.