The webs of Continuous Rigid Frame Bridge suffer from cracking generally. In this paper, the mechanical characteristics of the box girder with cracked webs were studied. With reference of ChongQing JiangJin bridge, the 3-D solid FEM that employed with the smeared crack model was used to analysis the crack distribution. The law of reduced local stiffness and global stiffness on box girder with cracked sections was studied. At the same time, A sensitive analysis was performed to assess the effects of the effective prestress and reinforcement ratio on the cracking resistance and the reduced stiffness.