Under the acid rain corrosion condition, the shear-bearing capacity of the pretension prestressed concrete beam will attenuate gradually with the stirrup corrosion and concrete deteriorate. Moreover, the stress corrosion cracking failure and the bond force degradation of the prestressed wires that caused by the aggravated corrosion mediator ingress will further increase the shear failure risk of the pretension prestressed concrete structure without any symptom. The paper presents a shear bearing capacity calculation model of the pretension prestressed concrete beam bridge and discuss the time-variation model of the stirrup corrosion considering the effective prestress attenuation under the acid rain corrosion condition. The analysis method on anti-shear reliability of existing pretension prestressed concrete beam bridges under the sodium sulfate corrosion condition is proposed then. The method will be used in the durability and safety evaluation of the shear-bearing capacity of the existing pretension prestressed concrete beam bridges in the corrosion environment with acid rain.