Aiming at the crack phenomena in prestressed concrete continuous box girder bridges at present, on the background of Modaomen Bridge in Guangdong province, the influence of shrinkage and creep on crack resistance for PC box girder bridges is studied and discussed in this thesis. In the three-dimensional finite analysis of the whole model, the principal stress response of the structure under the permanent load (dead load and prestressing force) and shrinkage and creep is studied, and the shortage of the plane truss software is pointed out.