The shear bearing capacity of pretensioning prestressed concrete beam bridge mainly depends on the stirrup and concrete of the beam, but the longitudinal pre-pressure plays a certain role for the shear bearing of the structure. Under the carbonization corrosion condition, the shear-bearing capacity of the pretensioning prestressed concrete beam will attenuate gradually with the stirrup corrosion and concrete deteriorate. And the risk of brittle shear failure will be increased with the enhanced reinforcement corrosion amount. The paper presents an anti-shear calculation model of the pretensioning prestressed concrete beam bridge, and discusses the time-variation model of the corrosion stirrup considering the effective prestress attenuation under the carbonization corrosion condition. The analysis method on the anti-shear reliability of existing pretensioning bridges under the corrosion condition is proposed then. The method will be used in the durability and safety evaluation of the shear-bearing capacity of the existing pretensioning prestressed concrete bridges.